From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: [PATCH v2 04/13] mm: free swp_entry in madvise_free Date: Wed, 4 Nov 2015 10:25:58 +0900 Message-ID: <1446600367-7976-5-git-send-email-minchan@kernel.org> References: <1446600367-7976-1-git-send-email-minchan@kernel.org> Return-path: In-Reply-To: <1446600367-7976-1-git-send-email-minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrew Morton Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Michael Kerrisk , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Hugh Dickins , Johannes Weiner , Rik van Riel , Mel Gorman , KOSAKI Motohiro , Jason Evans , Daniel Micay , "Kirill A. Shutemov" , Shaohua Li , Michal Hocko , yalin.wang2010-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Minchan Kim , Michal Hocko List-Id: linux-api@vger.kernel.org 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 Acked-by: Hugh Dickins Signed-off-by: Minchan Kim --- 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