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mm: do not shrink pages marked for reclaim by MADV_FREE

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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>
This commit is contained in:
Prakash Gupta 2018-11-20 18:36:20 +05:30 • committed by Faiyaz Mohammed
commit a25275e2bd
1 changed files with 12 additions and 0 deletions
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12
fs/proc/task_mmu.c
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@ -1742,6 +1742,18 @@ cont:
if (isolate_lru_page(compound_head(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));