[PATCH v2 04/13] mm: free swp_entry in madvise_free
From: Minchan Kim <hidden>
Date: 2015-11-04 01:26:13
Also in:
linux-mm, lkml
Subsystem:
memory management, memory mapping - madvise (memory advice), the rest · Maintainers:
Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, David Hildenbrand, Linus Torvalds
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
Acked-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Acked-by: Hugh Dickins <redacted>
Signed-off-by: Minchan Kim <redacted>
---
mm/madvise.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c
index a8813f7b37b3..6240a5de4a3a 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c@@ -270,6 +270,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, spinlock_t *ptl; pte_t *pte, ptent; struct page *page; + int nr_swap = 0; split_huge_page_pmd(vma, addr, pmd); if (pmd_trans_unstable(pmd))
@@ -280,8 +281,24 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, 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)
@@ -317,6 +334,13 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, } } + 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(pte - 1, ptl); cond_resched();
--
1.9.1