aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/vm/transhuge.txt
diff options
context:
space:
mode:
authorPatrick McHardy <kaber@trash.net>2013-03-31 18:10:34 +0200
committerPatrick McHardy <kaber@trash.net>2013-03-31 18:10:34 +0200
commit70711d223510ba1773cfe1d7770a56141c815ff8 (patch)
tree4a71f38a3a554ddecaa31b7d8c6bc49b7d1705b4 /Documentation/vm/transhuge.txt
parentd53b4ed072d9779cdf53582c46436dec06d0961f (diff)
parent19f949f52599ba7c3f67a5897ac6be14bfcb1200 (diff)
Merge tag 'v3.8' of /home/kaber/src/repos/linux
Linux 3.8 Signed-off-by: Patrick McHardy <kaber@trash.net> Conflicts: include/linux/Kbuild include/linux/netlink.h
Diffstat (limited to 'Documentation/vm/transhuge.txt')
-rw-r--r--Documentation/vm/transhuge.txt19
1 files changed, 17 insertions, 2 deletions
diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
index f734bb2a78d..8785fb87d9c 100644
--- a/Documentation/vm/transhuge.txt
+++ b/Documentation/vm/transhuge.txt
@@ -116,6 +116,13 @@ echo always >/sys/kernel/mm/transparent_hugepage/defrag
echo madvise >/sys/kernel/mm/transparent_hugepage/defrag
echo never >/sys/kernel/mm/transparent_hugepage/defrag
+By default kernel tries to use huge zero page on read page fault.
+It's possible to disable huge zero page by writing 0 or enable it
+back by writing 1:
+
+echo 0 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page
+echo 1 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page
+
khugepaged will be automatically started when
transparent_hugepage/enabled is set to "always" or "madvise, and it'll
be automatically shutdown if it's set to "never".
@@ -197,6 +204,14 @@ 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.
+thp_zero_page_alloc is incremented every time a huge zero page is
+ successfully allocated. It includes allocations which where
+ dropped due race with other allocation. Note, it doesn't count
+ every map of the huge zero page, only its allocation.
+
+thp_zero_page_alloc_failed is incremented if kernel fails to allocate
+ huge zero page and falls back to using small pages.
+
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
@@ -276,7 +291,7 @@ unaffected. libhugetlbfs will also work fine as usual.
== Graceful fallback ==
Code walking pagetables but unware about huge pmds can simply call
-split_huge_page_pmd(mm, pmd) where the pmd is the one returned by
+split_huge_page_pmd(vma, addr, pmd) where the pmd is the one returned by
pmd_offset. It's trivial to make the code transparent hugepage aware
by just grepping for "pmd_offset" and adding split_huge_page_pmd where
missing after pmd_offset returns the pmd. Thanks to the graceful
@@ -299,7 +314,7 @@ diff --git a/mm/mremap.c b/mm/mremap.c
return NULL;
pmd = pmd_offset(pud, addr);
-+ split_huge_page_pmd(mm, pmd);
++ split_huge_page_pmd(vma, addr, pmd);
if (pmd_none_or_clear_bad(pmd))
return NULL;