|author||Mel Gorman <firstname.lastname@example.org>||2012-05-29 15:06:45 -0700|
|committer||Linus Torvalds <email@example.com>||2012-05-29 16:22:23 -0700|
|parent||mm/page_alloc.c: cleanups (diff)|
mm: document the meminfo and vmstat fields of relevance to transparent hugepages
Update Documentation/vm/transhuge.txt and Documentation/filesystems/proc.txt with some information on monitoring transparent huge page usage and the associated overhead. Signed-off-by: Mel Gorman <firstname.lastname@example.org> Signed-off-by: Andrea Arcangeli <email@example.com> Signed-off-by: Andrew Morton <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com>
2 files changed, 64 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index ef088e55ab2e..912af6ce5626 100644
@@ -743,6 +743,7 @@ Committed_AS: 100056 kB
VmallocTotal: 112216 kB
VmallocUsed: 428 kB
VmallocChunk: 111088 kB
+AnonHugePages: 49152 kB
MemTotal: Total usable ram (i.e. physical ram minus a few reserved
bits and the kernel binary code)
@@ -776,6 +777,7 @@ VmallocChunk: 111088 kB
Dirty: Memory which is waiting to get written back to the disk
Writeback: Memory which is actively being written back to the disk
AnonPages: Non-file backed pages mapped into userspace page tables
+AnonHugePages: Non-file backed huge pages mapped into userspace page tables
Mapped: files which have been mmaped, such as libraries
Slab: in-kernel data structures cache
SReclaimable: Part of Slab, that might be reclaimed, such as caches
diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
index 29bdf62aac09..f734bb2a78dc 100644
@@ -166,6 +166,68 @@ behavior. So to make them effective you need to restart any
application that could have been using hugepages. This also applies to
the regions registered in khugepaged.
+== Monitoring usage ==
+The number of transparent huge pages currently used by the system is
+available by reading the AnonHugePages field in /proc/meminfo. To
+identify what applications are using transparent huge pages, it is
+necessary to read /proc/PID/smaps and count the AnonHugePages fields
+for each mapping. Note that reading the smaps file is expensive and
+reading it frequently will incur overhead.
+There are a number of counters in /proc/vmstat that may be used to
+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. This applies to both the
+ first time a page is faulted and for COW faults.
+thp_collapse_alloc is incremented by khugepaged when it has found
+ a range of pages to collapse into one huge page and has
+ successfully allocated a new huge page to store the data.
+thp_fault_fallback is incremented if a page fault fails to allocate
+ a huge page and instead falls back to using small pages.
+thp_collapse_alloc_failed is incremented if khugepaged found a range
+ of pages that should be collapsed into one huge page but failed
+ the allocation.
+thp_split is incremented every time a huge page is split into base
+ pages. This can happen for a variety of reasons but a common
+ reason is that a huge page is old and is being reclaimed.
+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
+monitor this overhead.
+compact_stall is incremented every time a process stalls to run
+ memory compaction so that a huge page is free for use.
+compact_success is incremented if the system compacted memory and
+ freed a huge page for use.
+compact_fail is incremented if the system tries to compact memory
+ but failed.
+compact_pages_moved is incremented each time a page is moved. If
+ this value is increasing rapidly, it implies that the system
+ is copying a lot of data to satisfy the huge page allocation.
+ It is possible that the cost of copying exceeds any savings
+ from reduced TLB misses.
+compact_pagemigrate_failed is incremented when the underlying mechanism
+ for moving a page failed.
+compact_blocks_moved is incremented each time memory compaction examines
+ a huge page aligned range of pages.
+It is possible to establish how long the stalls were using the function
+tracer to record how long was spent in __alloc_pages_nodemask and
+using the mm_page_alloc tracepoint to identify which allocations were
+for huge pages.
== get_user_pages and follow_page ==
get_user_pages and follow_page if run on a hugepage, will return the