The patch titled
Subject: mm/madvise.c: free swp_entry in madvise_free
has been added to the -mm tree. Its filename is
mm-free-swp_entry-in-madvise_free.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-free-swp_entry-in-madvise_free.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-free-swp_entry-in-madvise_free.patch
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From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: mm/madvise.c: free swp_entry in madvise_free
When I test below piece of code with 12 processes(ie, 512M * 12 = 6G
consume) on my (3G ram + 12 cpu + 8G swap, the madvise_free is siginficat
slower (ie, 2x times) than madvise_dontneed.
loop = 5;
mmap(512M);
while (loop--) {
memset(512M);
madvise(MADV_FREE or MADV_DONTNEED);
}
The reason is lots of swapin.
1) dontneed: 1,612 swapin
2) madvfree: 879,585 swapin
If we find hinted pages were already swapped out when syscall is called,
it's pointless to keep the swapped-out pages in pte. Instead, let's free
the cold page because swapin is more expensive than (alloc page +
zeroing).
With this patch, it reduced swapin from 879,585 to 1,878 so elapsed time
1) dontneed: 6.10user 233.50system 0:50.44elapsed
2) madvfree: 6.03user 401.17system 1:30.67elapsed
2) madvfree + below patch: 6.70user 339.14system 1:04.45elapsed
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: "Shaohua Li" <shli@xxxxxxxxxx>
Cc: <yalin.wang2010@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Chen Gang <gang.chen.5i5j@xxxxxxxxx>
Cc: Chris Zankel <chris@xxxxxxxxxx>
Cc: Daniel Micay <danielmicay@xxxxxxxxx>
Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>
Cc: Jason Evans <je@xxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Matt Turner <mattst88@xxxxxxxxx>
Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Cc: Mika Penttil <mika.penttila@xxxxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Roland Dreier <roland@xxxxxxxxxx>
Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/madvise.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff -puN mm/madvise.c~mm-free-swp_entry-in-madvise_free mm/madvise.c
--- a/mm/madvise.c~mm-free-swp_entry-in-madvise_free
+++ a/mm/madvise.c
@@ -270,6 +270,7 @@ static int madvise_free_pte_range(pmd_t
spinlock_t *ptl;
pte_t *orig_pte, *pte, ptent;
struct page *page;
+ int nr_swap = 0;
split_huge_pmd(vma, pmd, addr);
if (pmd_trans_unstable(pmd))
@@ -280,8 +281,24 @@ static int madvise_free_pte_range(pmd_t
for (; addr != end; pte++, addr += PAGE_SIZE) {
ptent = *pte;
- if (!pte_present(ptent))
+ if (pte_none(ptent))
continue;
+ /*
+ * If the pte has swp_entry, just clear page table to
+ * prevent swap-in which is more expensive rather than
+ * (page allocation + zeroing).
+ */
+ if (!pte_present(ptent)) {
+ swp_entry_t entry;
+
+ entry = pte_to_swp_entry(ptent);
+ if (non_swap_entry(entry))
+ continue;
+ nr_swap--;
+ free_swap_and_cache(entry);
+ pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
+ continue;
+ }
page = vm_normal_page(vma, addr, ptent);
if (!page)
@@ -355,6 +372,12 @@ static int madvise_free_pte_range(pmd_t
}
}
out:
+ if (nr_swap) {
+ if (current->mm == mm)
+ sync_mm_rss(mm);
+
+ add_mm_counter(mm, MM_SWAPENTS, nr_swap);
+ }
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(orig_pte, ptl);
cond_resched();
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
zram-pass-gfp-from-zcomp-frontend-to-backend.patch
mm-support-madvisemadv_free.patch
mm-support-madvisemadv_free-fix.patch
mm-define-madv_free-for-some-arches.patch
mm-free-swp_entry-in-madvise_free.patch
mm-move-lazily-freed-pages-to-inactive-list.patch
mm-mark-stable-page-dirty-in-ksm.patch
x86-add-pmd_-for-thp.patch
sparc-add-pmd_-for-thp.patch
powerpc-add-pmd_-for-thp.patch
arm-add-pmd_mkclean-for-thp.patch
arm64-add-pmd_mkclean-for-thp.patch
mm-dont-split-thp-page-when-syscall-is-called.patch
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