diff options
Diffstat (limited to 'Documentation/mm')
| -rw-r--r-- | Documentation/mm/allocation-profiling.rst | 100 | ||||
| -rw-r--r-- | Documentation/mm/arch_pgtable_helpers.rst | 6 | ||||
| -rw-r--r-- | Documentation/mm/damon/design.rst | 114 | ||||
| -rw-r--r-- | Documentation/mm/damon/maintainer-profile.rst | 17 | ||||
| -rw-r--r-- | Documentation/mm/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/mm/page_cache.rst | 10 | ||||
| -rw-r--r-- | Documentation/mm/page_frags.rst | 2 | ||||
| -rw-r--r-- | Documentation/mm/page_owner.rst | 48 | ||||
| -rw-r--r-- | Documentation/mm/page_table_check.rst | 9 | ||||
| -rw-r--r-- | Documentation/mm/slub.rst | 62 | ||||
| -rw-r--r-- | Documentation/mm/transhuge.rst | 12 | ||||
| -rw-r--r-- | Documentation/mm/vmemmap_dedup.rst | 22 |
12 files changed, 305 insertions, 98 deletions
diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst new file mode 100644 index 0000000000..d3b733b41a --- /dev/null +++ b/Documentation/mm/allocation-profiling.rst @@ -0,0 +1,100 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=========================== +MEMORY ALLOCATION PROFILING +=========================== + +Low overhead (suitable for production) accounting of all memory allocations, +tracked by file and line number. + +Usage: +kconfig options: +- CONFIG_MEM_ALLOC_PROFILING + +- CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT + +- CONFIG_MEM_ALLOC_PROFILING_DEBUG + adds warnings for allocations that weren't accounted because of a + missing annotation + +Boot parameter: + sysctl.vm.mem_profiling=0|1|never + + When set to "never", memory allocation profiling overhead is minimized and it + cannot be enabled at runtime (sysctl becomes read-only). + When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y, default value is "1". + When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n, default value is "never". + +sysctl: + /proc/sys/vm/mem_profiling + +Runtime info: + /proc/allocinfo + +Example output:: + + root@moria-kvm:~# sort -g /proc/allocinfo|tail|numfmt --to=iec + 2.8M 22648 fs/kernfs/dir.c:615 func:__kernfs_new_node + 3.8M 953 mm/memory.c:4214 func:alloc_anon_folio + 4.0M 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start + 4.1M 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable + 6.0M 1532 mm/filemap.c:1919 func:__filemap_get_folio + 8.8M 2785 kernel/fork.c:307 func:alloc_thread_stack_node + 13M 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs + 14M 3520 mm/mm_init.c:2530 func:alloc_large_system_hash + 15M 3656 mm/readahead.c:247 func:page_cache_ra_unbounded + 55M 4887 mm/slub.c:2259 func:alloc_slab_page + 122M 31168 mm/page_ext.c:270 func:alloc_page_ext + +=================== +Theory of operation +=================== + +Memory allocation profiling builds off of code tagging, which is a library for +declaring static structs (that typically describe a file and line number in +some way, hence code tagging) and then finding and operating on them at runtime, +- i.e. iterating over them to print them in debugfs/procfs. + +To add accounting for an allocation call, we replace it with a macro +invocation, alloc_hooks(), that +- declares a code tag +- stashes a pointer to it in task_struct +- calls the real allocation function +- and finally, restores the task_struct alloc tag pointer to its previous value. + +This allows for alloc_hooks() calls to be nested, with the most recent one +taking effect. This is important for allocations internal to the mm/ code that +do not properly belong to the outer allocation context and should be counted +separately: for example, slab object extension vectors, or when the slab +allocates pages from the page allocator. + +Thus, proper usage requires determining which function in an allocation call +stack should be tagged. There are many helper functions that essentially wrap +e.g. kmalloc() and do a little more work, then are called in multiple places; +we'll generally want the accounting to happen in the callers of these helpers, +not in the helpers themselves. + +To fix up a given helper, for example foo(), do the following: +- switch its allocation call to the _noprof() version, e.g. kmalloc_noprof() + +- rename it to foo_noprof() + +- define a macro version of foo() like so: + + #define foo(...) alloc_hooks(foo_noprof(__VA_ARGS__)) + +It's also possible to stash a pointer to an alloc tag in your own data structures. + +Do this when you're implementing a generic data structure that does allocations +"on behalf of" some other code - for example, the rhashtable code. This way, +instead of seeing a large line in /proc/allocinfo for rhashtable.c, we can +break it out by rhashtable type. + +To do so: +- Hook your data structure's init function, like any other allocation function. + +- Within your init function, use the convenience macro alloc_tag_record() to + record alloc tag in your data structure. + +- Then, use the following form for your allocations: + alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...)) diff --git a/Documentation/mm/arch_pgtable_helpers.rst b/Documentation/mm/arch_pgtable_helpers.rst index 2466d3363a..ad50ca6f49 100644 --- a/Documentation/mm/arch_pgtable_helpers.rst +++ b/Documentation/mm/arch_pgtable_helpers.rst @@ -140,7 +140,8 @@ PMD Page Table Helpers +---------------------------+--------------------------------------------------+ | pmd_swp_clear_soft_dirty | Clears a soft dirty swapped PMD | +---------------------------+--------------------------------------------------+ -| pmd_mkinvalid | Invalidates a mapped PMD [1] | +| pmd_mkinvalid | Invalidates a present PMD; do not call for | +| | non-present PMD [1] | +---------------------------+--------------------------------------------------+ | pmd_set_huge | Creates a PMD huge mapping | +---------------------------+--------------------------------------------------+ @@ -196,7 +197,8 @@ PUD Page Table Helpers +---------------------------+--------------------------------------------------+ | pud_mkdevmap | Creates a ZONE_DEVICE mapped PUD | +---------------------------+--------------------------------------------------+ -| pud_mkinvalid | Invalidates a mapped PUD [1] | +| pud_mkinvalid | Invalidates a present PUD; do not call for | +| | non-present PUD [1] | +---------------------------+--------------------------------------------------+ | pud_set_huge | Creates a PUD huge mapping | +---------------------------+--------------------------------------------------+ diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst index 1bb69524a6..3df3872499 100644 --- a/Documentation/mm/damon/design.rst +++ b/Documentation/mm/damon/design.rst @@ -31,6 +31,8 @@ DAMON subsystem is configured with three layers including interfaces for the user space, on top of the core layer. +.. _damon_design_configurable_operations_set: + Configurable Operations Set --------------------------- @@ -63,6 +65,8 @@ modules that built on top of the core layer using the API, which can be easily used by the user space end users. +.. _damon_operations_set: + Operations Set Layer ==================== @@ -71,16 +75,26 @@ The monitoring operations are defined in two parts: 1. Identification of the monitoring target address range for the address space. 2. Access check of specific address range in the target space. -DAMON currently provides the implementations of the operations for the physical -and virtual address spaces. Below two subsections describe how those work. +DAMON currently provides below three operation sets. Below two subsections +describe how those work. + + - vaddr: Monitor virtual address spaces of specific processes + - fvaddr: Monitor fixed virtual address ranges + - paddr: Monitor the physical address space of the system + + .. _damon_design_vaddr_target_regions_construction: VMA-based Target Address Range Construction ------------------------------------------- -This is only for the virtual address space monitoring operations -implementation. That for the physical address space simply asks users to -manually set the monitoring target address ranges. +A mechanism of ``vaddr`` DAMON operations set that automatically initializes +and updates the monitoring target address regions so that entire memory +mappings of the target processes can be covered. + +This mechanism is only for the ``vaddr`` operations set. In cases of +``fvaddr`` and ``paddr`` operation sets, users are asked to manually set the +monitoring target address ranges. Only small parts in the super-huge virtual address space of the processes are mapped to the physical memory and accessed. Thus, tracking the unmapped @@ -294,9 +308,29 @@ not mandated to support all actions of the list. Hence, the availability of specific DAMOS action depends on what operations set is selected to be used together. -Applying an action to a region is considered as changing the region's -characteristics. Hence, DAMOS resets the age of regions when an action is -applied to those. +The list of the supported actions, their meaning, and DAMON operations sets +that supports each action are as below. + + - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``pageout``: Reclaim the region. + Supported by ``vaddr``, ``fvaddr`` and ``paddr`` operations set. + - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``lru_prio``: Prioritize the region on its LRU lists. + Supported by ``paddr`` operations set. + - ``lru_deprio``: Deprioritize the region on its LRU lists. + Supported by ``paddr`` operations set. + - ``stat``: Do nothing but count the statistics. + Supported by all operations sets. + +Applying the actions except ``stat`` to a region is considered as changing the +region's characteristics. Hence, DAMOS resets the age of regions when any such +actions are applied to those. .. _damon_design_damos_access_pattern: @@ -364,12 +398,28 @@ Aim-oriented Feedback-driven Auto-tuning ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Automatic feedback-driven quota tuning. Instead of setting the absolute quota -value, users can repeatedly provide numbers representing how much of their goal -for the scheme is achieved as feedback. DAMOS then automatically tunes the +value, users can specify the metric of their interest, and what target value +they want the metric value to be. DAMOS then automatically tunes the aggressiveness (the quota) of the corresponding scheme. For example, if DAMOS is under achieving the goal, DAMOS automatically increases the quota. If DAMOS is over achieving the goal, it decreases the quota. +The goal can be specified with three parameters, namely ``target_metric``, +``target_value``, and ``current_value``. The auto-tuning mechanism tries to +make ``current_value`` of ``target_metric`` be same to ``target_value``. +Currently, two ``target_metric`` are provided. + +- ``user_input``: User-provided value. Users could use any metric that they + has interest in for the value. Use space main workload's latency or + throughput, system metrics like free memory ratio or memory pressure stall + time (PSI) could be examples. Note that users should explicitly set + ``current_value`` on their own in this case. In other words, users should + repeatedly provide the feedback. +- ``some_mem_psi_us``: System-wide ``some`` memory pressure stall information + in microseconds that measured from last quota reset to next quota reset. + DAMOS does the measurement on its own, so only ``target_value`` need to be + set by users at the initial time. In other words, DAMOS does self-feedback. + .. _damon_design_damos_watermarks: @@ -411,24 +461,32 @@ number of filters for each scheme. Each filter specifies the type of target memory, and whether it should exclude the memory of the type (filter-out), or all except the memory of the type (filter-in). -Currently, anonymous page, memory cgroup, address range, and DAMON monitoring -target type filters are supported by the feature. Some filter target types -require additional arguments. The memory cgroup filter type asks users to -specify the file path of the memory cgroup for the filter. The address range -type asks the start and end addresses of the range. The DAMON monitoring -target type asks the index of the target from the context's monitoring targets -list. Hence, users can apply specific schemes to only anonymous pages, -non-anonymous pages, pages of specific cgroups, all pages excluding those of -specific cgroups, pages in specific address range, pages in specific DAMON -monitoring targets, and any combination of those. - -To handle filters efficiently, the address range and DAMON monitoring target -type filters are handled by the core layer, while others are handled by -operations set. If a memory region is filtered by a core layer-handled filter, -it is not counted as the scheme has tried to the region. In contrast, if a -memory regions is filtered by an operations set layer-handled filter, it is -counted as the scheme has tried. The difference in accounting leads to changes -in the statistics. +For efficient handling of filters, some types of filters are handled by the +core layer, while others are handled by operations set. In the latter case, +hence, support of the filter types depends on the DAMON operations set. In +case of the core layer-handled filters, the memory regions that excluded by the +filter are not counted as the scheme has tried to the region. In contrast, if +a memory regions is filtered by an operations set layer-handled filter, it is +counted as the scheme has tried. This difference affects the statistics. + +Below types of filters are currently supported. + +- anonymous page + - Applied to pages that containing data that not stored in files. + - Handled by operations set layer. Supported by only ``paddr`` set. +- memory cgroup + - Applied to pages that belonging to a given cgroup. + - Handled by operations set layer. Supported by only ``paddr`` set. +- young page + - Applied to pages that are accessed after the last access check from the + scheme. + - Handled by operations set layer. Supported by only ``paddr`` set. +- address range + - Applied to pages that belonging to a given address range. + - Handled by the core logic. +- DAMON monitoring target + - Applied to pages that belonging to a given DAMON monitoring target. + - Handled by the core logic. Application Programming Interface diff --git a/Documentation/mm/damon/maintainer-profile.rst b/Documentation/mm/damon/maintainer-profile.rst index a84c14e590..8213cf61d3 100644 --- a/Documentation/mm/damon/maintainer-profile.rst +++ b/Documentation/mm/damon/maintainer-profile.rst @@ -20,9 +20,10 @@ management subsystem maintainer. After more sufficient tests, the patches will be queued in mm-stable [3]_ , and finally pull-requested to the mainline by the memory management subsystem maintainer. -Note again the patches for review should be made against the mm-unstable -tree[1] whenever possible. damon/next is only for preview of others' works in -progress. +Note again the patches for mm-unstable tree [1]_ are queued by the memory +management subsystem maintainer. If the patches requires some patches in +damon/next tree [2]_ which not yet merged in mm-unstable, please make sure the +requirement is clearly specified. Submit checklist addendum ------------------------- @@ -41,16 +42,16 @@ Further doing below and putting the results will be helpful. Key cycle dates --------------- -Patches can be sent anytime. Key cycle dates of the mm-unstable[1] and -mm-stable[3] trees depend on the memory management subsystem maintainer. +Patches can be sent anytime. Key cycle dates of the mm-unstable [1]_ and +mm-stable [3]_ trees depend on the memory management subsystem maintainer. Review cadence -------------- The DAMON maintainer does the work on the usual work hour (09:00 to 17:00, -Mon-Fri) in PST. The response to patches will occasionally be slow. Do not -hesitate to send a ping if you have not heard back within a week of sending a -patch. +Mon-Fri) in PT (Pacific Time). The response to patches will occasionally be +slow. Do not hesitate to send a ping if you have not heard back within a week +of sending a patch. .. [1] https://git.kernel.org/akpm/mm/h/mm-unstable diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst index 31d2ac3064..48b9b559ca 100644 --- a/Documentation/mm/index.rst +++ b/Documentation/mm/index.rst @@ -26,6 +26,7 @@ see the :doc:`admin guide <../admin-guide/mm/index>`. page_cache shmfs oom + allocation-profiling Legacy Documentation ==================== diff --git a/Documentation/mm/page_cache.rst b/Documentation/mm/page_cache.rst index 75eba7c431..138d61f869 100644 --- a/Documentation/mm/page_cache.rst +++ b/Documentation/mm/page_cache.rst @@ -3,3 +3,13 @@ ========== Page Cache ========== + +The page cache is the primary way that the user and the rest of the kernel +interact with filesystems. It can be bypassed (e.g. with O_DIRECT), +but normal reads, writes and mmaps go through the page cache. + +Folios +====== + +The folio is the unit of memory management within the page cache. +Operations diff --git a/Documentation/mm/page_frags.rst b/Documentation/mm/page_frags.rst index a81617e688..503ca6cdb8 100644 --- a/Documentation/mm/page_frags.rst +++ b/Documentation/mm/page_frags.rst @@ -25,7 +25,7 @@ to be disabled when executing the fragment allocation. The network stack uses two separate caches per CPU to handle fragment allocation. The netdev_alloc_cache is used by callers making use of the netdev_alloc_frag and __netdev_alloc_skb calls. The napi_alloc_cache is -used by callers of the __napi_alloc_frag and __napi_alloc_skb calls. The +used by callers of the __napi_alloc_frag and napi_alloc_skb calls. The main difference between these two calls is the context in which they may be called. The "netdev" prefixed functions are usable in any context as these functions will disable interrupts, while the "napi" prefixed functions are diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst index 62e3f7ab23..3a45a20fc0 100644 --- a/Documentation/mm/page_owner.rst +++ b/Documentation/mm/page_owner.rst @@ -24,6 +24,11 @@ fragmentation statistics can be obtained through gfp flag information of each page. It is already implemented and activated if page owner is enabled. Other usages are more than welcome. +It can also be used to show all the stacks and their current number of +allocated base pages, which gives us a quick overview of where the memory +is going without the need to screen through all the pages and match the +allocation and free operation. + page owner is disabled by default. So, if you'd like to use it, you need to add "page_owner=on" to your boot cmdline. If the kernel is built with page owner and page owner is disabled in runtime due to not enabling @@ -68,6 +73,49 @@ Usage 4) Analyze information from page owner:: + cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt + cat stacks.txt + post_alloc_hook+0x177/0x1a0 + get_page_from_freelist+0xd01/0xd80 + __alloc_pages+0x39e/0x7e0 + allocate_slab+0xbc/0x3f0 + ___slab_alloc+0x528/0x8a0 + kmem_cache_alloc+0x224/0x3b0 + sk_prot_alloc+0x58/0x1a0 + sk_alloc+0x32/0x4f0 + inet_create+0x427/0xb50 + __sock_create+0x2e4/0x650 + inet_ctl_sock_create+0x30/0x180 + igmp_net_init+0xc1/0x130 + ops_init+0x167/0x410 + setup_net+0x304/0xa60 + copy_net_ns+0x29b/0x4a0 + create_new_namespaces+0x4a1/0x820 + nr_base_pages: 16 + ... + ... + echo 7000 > /sys/kernel/debug/page_owner_stacks/count_threshold + cat /sys/kernel/debug/page_owner_stacks/show_stacks> stacks_7000.txt + cat stacks_7000.txt + post_alloc_hook+0x177/0x1a0 + get_page_from_freelist+0xd01/0xd80 + __alloc_pages+0x39e/0x7e0 + alloc_pages_mpol+0x22e/0x490 + folio_alloc+0xd5/0x110 + filemap_alloc_folio+0x78/0x230 + page_cache_ra_order+0x287/0x6f0 + filemap_get_pages+0x517/0x1160 + filemap_read+0x304/0x9f0 + xfs_file_buffered_read+0xe6/0x1d0 [xfs] + xfs_file_read_iter+0x1f0/0x380 [xfs] + __kernel_read+0x3b9/0x730 + kernel_read_file+0x309/0x4d0 + __do_sys_finit_module+0x381/0x730 + do_syscall_64+0x8d/0x150 + entry_SYSCALL_64_after_hwframe+0x62/0x6a + nr_base_pages: 20824 + ... + cat /sys/kernel/debug/page_owner > page_owner_full.txt ./page_owner_sort page_owner_full.txt sorted_page_owner.txt diff --git a/Documentation/mm/page_table_check.rst b/Documentation/mm/page_table_check.rst index c12838ce6b..c59f22eb6a 100644 --- a/Documentation/mm/page_table_check.rst +++ b/Documentation/mm/page_table_check.rst @@ -14,7 +14,7 @@ Page table check performs extra verifications at the time when new pages become accessible from the userspace by getting their page table entries (PTEs PMDs etc.) added into the table. -In case of detected corruption, the kernel is crashed. There is a small +In case of most detected corruption, the kernel is crashed. There is a small performance and memory overhead associated with the page table check. Therefore, it is disabled by default, but can be optionally enabled on systems where the extra hardening outweighs the performance costs. Also, because page table check @@ -22,6 +22,13 @@ is synchronous, it can help with debugging double map memory corruption issues, by crashing kernel at the time wrong mapping occurs instead of later which is often the case with memory corruptions bugs. +It can also be used to do page table entry checks over various flags, dump +warnings when illegal combinations of entry flags are detected. Currently, +userfaultfd is the only user of such to sanity check wr-protect bit against +any writable flags. Illegal flag combinations will not directly cause data +corruption in this case immediately, but that will cause read-only data to +be writable, leading to corrupt when the page content is later modified. + Double mapping detection logic ============================== diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst index be75971532..60d350d083 100644 --- a/Documentation/mm/slub.rst +++ b/Documentation/mm/slub.rst @@ -9,7 +9,7 @@ SLUB can enable debugging only for selected slabs in order to avoid an impact on overall system performance which may make a bug more difficult to find. -In order to switch debugging on one can add an option ``slub_debug`` +In order to switch debugging on one can add an option ``slab_debug`` to the kernel command line. That will enable full debugging for all slabs. @@ -26,16 +26,16 @@ be enabled on the command line. F.e. no tracking information will be available without debugging on and validation can only partially be performed if debugging was not switched on. -Some more sophisticated uses of slub_debug: +Some more sophisticated uses of slab_debug: ------------------------------------------- -Parameters may be given to ``slub_debug``. If none is specified then full +Parameters may be given to ``slab_debug``. If none is specified then full debugging is enabled. Format: -slub_debug=<Debug-Options> +slab_debug=<Debug-Options> Enable options for all slabs -slub_debug=<Debug-Options>,<slab name1>,<slab name2>,... +slab_debug=<Debug-Options>,<slab name1>,<slab name2>,... Enable options only for select slabs (no spaces after a comma) @@ -60,44 +60,44 @@ Possible debug options are:: F.e. in order to boot just with sanity checks and red zoning one would specify:: - slub_debug=FZ + slab_debug=FZ Trying to find an issue in the dentry cache? Try:: - slub_debug=,dentry + slab_debug=,dentry to only enable debugging on the dentry cache. You may use an asterisk at the end of the slab name, in order to cover all slabs with the same prefix. For example, here's how you can poison the dentry cache as well as all kmalloc slabs:: - slub_debug=P,kmalloc-*,dentry + slab_debug=P,kmalloc-*,dentry Red zoning and tracking may realign the slab. We can just apply sanity checks to the dentry cache with:: - slub_debug=F,dentry + slab_debug=F,dentry Debugging options may require the minimum possible slab order to increase as a result of storing the metadata (for example, caches with PAGE_SIZE object -sizes). This has a higher liklihood of resulting in slab allocation errors +sizes). This has a higher likelihood of resulting in slab allocation errors in low memory situations or if there's high fragmentation of memory. To switch off debugging for such caches by default, use:: - slub_debug=O + slab_debug=O You can apply different options to different list of slab names, using blocks of options. This will enable red zoning for dentry and user tracking for kmalloc. All other slabs will not get any debugging enabled:: - slub_debug=Z,dentry;U,kmalloc-* + slab_debug=Z,dentry;U,kmalloc-* You can also enable options (e.g. sanity checks and poisoning) for all caches except some that are deemed too performance critical and don't need to be debugged by specifying global debug options followed by a list of slab names with "-" as options:: - slub_debug=FZ;-,zs_handle,zspage + slab_debug=FZ;-,zs_handle,zspage The state of each debug option for a slab can be found in the respective files under:: @@ -105,7 +105,7 @@ under:: /sys/kernel/slab/<slab name>/ If the file contains 1, the option is enabled, 0 means disabled. The debug -options from the ``slub_debug`` parameter translate to the following files:: +options from the ``slab_debug`` parameter translate to the following files:: F sanity_checks Z red_zone @@ -129,7 +129,7 @@ in order to reduce overhead and increase cache hotness of objects. Slab validation =============== -SLUB can validate all object if the kernel was booted with slub_debug. In +SLUB can validate all object if the kernel was booted with slab_debug. In order to do so you must have the ``slabinfo`` tool. Then you can do :: @@ -150,29 +150,29 @@ list_lock once in a while to deal with partial slabs. That overhead is governed by the order of the allocation for each slab. The allocations can be influenced by kernel parameters: -.. slub_min_objects=x (default 4) -.. slub_min_order=x (default 0) -.. slub_max_order=x (default 3 (PAGE_ALLOC_COSTLY_ORDER)) +.. slab_min_objects=x (default: automatically scaled by number of cpus) +.. slab_min_order=x (default 0) +.. slab_max_order=x (default 3 (PAGE_ALLOC_COSTLY_ORDER)) -``slub_min_objects`` +``slab_min_objects`` allows to specify how many objects must at least fit into one slab in order for the allocation order to be acceptable. In general slub will be able to perform this number of allocations on a slab without consulting centralized resources (list_lock) where contention may occur. -``slub_min_order`` +``slab_min_order`` specifies a minimum order of slabs. A similar effect like - ``slub_min_objects``. + ``slab_min_objects``. -``slub_max_order`` - specified the order at which ``slub_min_objects`` should no +``slab_max_order`` + specified the order at which ``slab_min_objects`` should no longer be checked. This is useful to avoid SLUB trying to - generate super large order pages to fit ``slub_min_objects`` + generate super large order pages to fit ``slab_min_objects`` of a slab cache with large object sizes into one high order page. Setting command line parameter ``debug_guardpage_minorder=N`` (N > 0), forces setting - ``slub_max_order`` to 0, what cause minimum possible order of + ``slab_max_order`` to 0, what cause minimum possible order of slabs allocation. SLUB Debug output @@ -219,7 +219,7 @@ Here is a sample of slub debug output:: FIX kmalloc-8: Restoring Redzone 0xc90f6d28-0xc90f6d2b=0xcc If SLUB encounters a corrupted object (full detection requires the kernel -to be booted with slub_debug) then the following output will be dumped +to be booted with slab_debug) then the following output will be dumped into the syslog: 1. Description of the problem encountered @@ -239,7 +239,7 @@ into the syslog: pid=<pid of the process> (Object allocation / free information is only available if SLAB_STORE_USER is - set for the slab. slub_debug sets that option) + set for the slab. slab_debug sets that option) 2. The object contents if an object was involved. @@ -262,7 +262,7 @@ into the syslog: the object boundary. (Redzone information is only available if SLAB_RED_ZONE is set. - slub_debug sets that option) + slab_debug sets that option) Padding <address> : <bytes> Unused data to fill up the space in order to get the next object @@ -296,7 +296,7 @@ Emergency operations Minimal debugging (sanity checks alone) can be enabled by booting with:: - slub_debug=F + slab_debug=F This will be generally be enough to enable the resiliency features of slub which will keep the system running even if a bad kernel component will @@ -311,13 +311,13 @@ and enabling debugging only for that cache I.e.:: - slub_debug=F,dentry + slab_debug=F,dentry If the corruption occurs by writing after the end of the object then it may be advisable to enable a Redzone to avoid corrupting the beginning of other objects:: - slub_debug=FZ,dentry + slab_debug=FZ,dentry Extended slabinfo mode and plotting =================================== diff --git a/Documentation/mm/transhuge.rst b/Documentation/mm/transhuge.rst index 93c9239b9e..1ba0ad6324 100644 --- a/Documentation/mm/transhuge.rst +++ b/Documentation/mm/transhuge.rst @@ -116,14 +116,14 @@ pages: succeeds on tail pages. - map/unmap of a PMD entry for the whole THP increment/decrement - folio->_entire_mapcount and also increment/decrement - folio->_nr_pages_mapped by ENTIRELY_MAPPED when _entire_mapcount - goes from -1 to 0 or 0 to -1. + folio->_entire_mapcount, increment/decrement folio->_large_mapcount + and also increment/decrement folio->_nr_pages_mapped by ENTIRELY_MAPPED + when _entire_mapcount goes from -1 to 0 or 0 to -1. - map/unmap of individual pages with PTE entry increment/decrement - page->_mapcount and also increment/decrement folio->_nr_pages_mapped - when page->_mapcount goes from -1 to 0 or 0 to -1 as this counts - the number of pages mapped by PTE. + page->_mapcount, increment/decrement folio->_large_mapcount and also + increment/decrement folio->_nr_pages_mapped when page->_mapcount goes + from -1 to 0 or 0 to -1 as this counts the number of pages mapped by PTE. split_huge_page internally has to distribute the refcounts in the head page to the tail pages before clearing all PG_head/tail bits from the page diff --git a/Documentation/mm/vmemmap_dedup.rst b/Documentation/mm/vmemmap_dedup.rst index 593ede6d31..b4a55b6569 100644 --- a/Documentation/mm/vmemmap_dedup.rst +++ b/Documentation/mm/vmemmap_dedup.rst @@ -180,27 +180,7 @@ this correctly. There is only **one** head ``struct page``, the tail ``struct page`` with ``PG_head`` are fake head ``struct page``. We need an approach to distinguish between those two different types of ``struct page`` so that ``compound_head()`` can return the real head ``struct page`` when the -parameter is the tail ``struct page`` but with ``PG_head``. The following code -snippet describes how to distinguish between real and fake head ``struct page``. - -.. code-block:: c - - if (test_bit(PG_head, &page->flags)) { - unsigned long head = READ_ONCE(page[1].compound_head); - - if (head & 1) { - if (head == (unsigned long)page + 1) - /* head struct page */ - else - /* tail struct page */ - } else { - /* head struct page */ - } - } - -We can safely access the field of the **page[1]** with ``PG_head`` because the -page is a compound page composed with at least two contiguous pages. -The implementation refers to ``page_fixed_fake_head()``. +parameter is the tail ``struct page`` but with ``PG_head``. Device DAX ========== |