From ba76149f47d8c939efa0acc07a191237af900471 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Thu, 13 Jan 2011 15:46:58 -0800 Subject: thp: khugepaged Add khugepaged to relocate fragmented pages into hugepages if new hugepages become available. (this is indipendent of the defrag logic that will have to make new hugepages available) The fundamental reason why khugepaged is unavoidable, is that some memory can be fragmented and not everything can be relocated. So when a virtual machine quits and releases gigabytes of hugepages, we want to use those freely available hugepages to create huge-pmd in the other virtual machines that may be running on fragmented memory, to maximize the CPU efficiency at all times. The scan is slow, it takes nearly zero cpu time, except when it copies data (in which case it means we definitely want to pay for that cpu time) so it seems a good tradeoff. In addition to the hugepages being released by other process releasing memory, we have the strong suspicion that the performance impact of potentially defragmenting hugepages during or before each page fault could lead to more performance inconsistency than allocating small pages at first and having them collapsed into large pages later... if they prove themselfs to be long lived mappings (khugepaged scan is slow so short lived mappings have low probability to run into khugepaged if compared to long lived mappings). Signed-off-by: Andrea Arcangeli Acked-by: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'kernel') diff --git a/kernel/fork.c b/kernel/fork.c index f78f50ba6cb2..25e429152ddc 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -66,6 +66,7 @@ #include #include #include +#include #include #include @@ -328,6 +329,9 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm) rb_parent = NULL; pprev = &mm->mmap; retval = ksm_fork(mm, oldmm); + if (retval) + goto out; + retval = khugepaged_fork(mm, oldmm); if (retval) goto out; @@ -546,6 +550,7 @@ void mmput(struct mm_struct *mm) if (atomic_dec_and_test(&mm->mm_users)) { exit_aio(mm); ksm_exit(mm); + khugepaged_exit(mm); /* must run before exit_mmap */ exit_mmap(mm); set_mm_exe_file(mm, NULL); if (!list_empty(&mm->mmlist)) { -- cgit v1.2.1