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-rw-r--r--Documentation/admin-guide/mm/transhuge.rst35
1 files changed, 32 insertions, 3 deletions
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 04eb45a2f9..d414d3f559 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -278,7 +278,8 @@ collapsed, resulting fewer pages being collapsed into
THPs, and lower memory access performance.
``max_ptes_shared`` specifies how many pages can be shared across multiple
-processes. Exceeding the number would block the collapse::
+processes. khugepaged might treat pages of THPs as shared if any page of
+that THP is shared. Exceeding the number would block the collapse::
/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_shared
@@ -369,7 +370,7 @@ monitor how successfully the system is providing huge pages for use.
thp_fault_alloc
is incremented every time a huge page is successfully
- allocated to handle a page fault.
+ allocated and charged to handle a page fault.
thp_collapse_alloc
is incremented by khugepaged when it has found
@@ -377,7 +378,7 @@ thp_collapse_alloc
successfully allocated a new huge page to store the data.
thp_fault_fallback
- is incremented if a page fault fails to allocate
+ is incremented if a page fault fails to allocate or charge
a huge page and instead falls back to using small pages.
thp_fault_fallback_charge
@@ -447,6 +448,34 @@ thp_swpout_fallback
Usually because failed to allocate some continuous swap space
for the huge page.
+In /sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/stats, There are
+also individual counters for each huge page size, which can be utilized to
+monitor the system's effectiveness in providing huge pages for usage. Each
+counter has its own corresponding file.
+
+anon_fault_alloc
+ is incremented every time a huge page is successfully
+ allocated and charged to handle a page fault.
+
+anon_fault_fallback
+ is incremented if a page fault fails to allocate or charge
+ a huge page and instead falls back to using huge pages with
+ lower orders or small pages.
+
+anon_fault_fallback_charge
+ is incremented if a page fault fails to charge a huge page and
+ instead falls back to using huge pages with lower orders or
+ small pages even though the allocation was successful.
+
+swpout
+ is incremented every time a huge page is swapped out in one
+ piece without splitting.
+
+swpout_fallback
+ is incremented if a huge page has to be split before swapout.
+ Usually because failed to allocate some continuous swap space
+ for the huge page.
+
As the system ages, allocating huge pages may be expensive as the
system uses memory compaction to copy data around memory to free a
huge page for use. There are some counters in ``/proc/vmstat`` to help