Commit 482f5ddd authored Nov 20, 2018 by Prakash Gupta Committed by Gerrit - the friendly Code Review server May 24, 2019

mm: do not shrink pages marked for reclaim by MADV_FREE

MADV_FREE clears pte dirty bit and then marks the page lazyfree (clear
SwapBacked). PPR increments ISOLATE_FILES count, then isolates page and
invokes a reclaim. Inbetween if this lazyfreed page is touched by user then
it becomes dirty. PPR in shrink_page_list in try_to_unmap finds the page
dirty, marks it back as PageSwapBacked and skips reclaim. As PageSwapBacked
set, PPR identifies the page as anon and decrements ISOLATED_ANON, thus
creating isolated count mismatch.

This results in too_many_isolated() check causing delay in reclaim. Skip
reclaiming lazyfreed pages in PPR path.

Change-Id: I87223c4fa492c5e373ac48f116384b5de03da9fa
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>

parent 0ac526e0

fs/proc/task_mmu.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -1665,6 +1665,18 @@ static int reclaim_pte_range(pmd_t *pmd, unsigned long addr,
		if (isolate_lru_page(page))
		continue;

		/* MADV_FREE clears pte dirty bit and then marks the page
		* lazyfree (clear SwapBacked). Inbetween if this lazyfreed page
		* is touched by user then it becomes dirty. PPR in
		* shrink_page_list in try_to_unmap finds the page dirty, marks
		* it back as PageSwapBacked and skips reclaim. This can cause
		* isolated count mismatch.
		*/
		if (PageAnon(page) && !PageSwapBacked(page)) {
		putback_lru_page(page);
		continue;
		}

		list_add(&page->lru, &page_list);
		inc_node_page_state(page, NR_ISOLATED_ANON +
		page_is_file_cache(page));