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@xxxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> --- mm/madvise.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/mm/madvise.c b/mm/madvise.c index 7b5c6f648fdb..c8e23102fc99 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) @@ -327,6 +344,13 @@ 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 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html