From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f197.google.com (mail-wj0-f197.google.com [209.85.210.197]) by kanga.kvack.org (Postfix) with ESMTP id C39646B0260 for ; Mon, 23 Jan 2017 13:17:09 -0500 (EST) Received: by mail-wj0-f197.google.com with SMTP id jz4so28133949wjb.5 for ; Mon, 23 Jan 2017 10:17:09 -0800 (PST) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id d21si19719942wrc.113.2017.01.23.10.17.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Jan 2017 10:17:08 -0800 (PST) From: Johannes Weiner Subject: [PATCH 4/5] mm: vmscan: only write dirty pages that the scanner has seen twice Date: Mon, 23 Jan 2017 13:16:40 -0500 Message-Id: <20170123181641.23938-5-hannes@cmpxchg.org> In-Reply-To: <20170123181641.23938-1-hannes@cmpxchg.org> References: <20170123181641.23938-1-hannes@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Dirty pages can easily reach the end of the LRU while there are still clean pages to reclaim around. Don't let kswapd write them back just because there are a lot of them. It costs more CPU to find the clean pages, but that's almost certainly better than to disrupt writeback from the flushers with LRU-order single-page writes from reclaim. And the flushers have been woken up by that point, so we spend IO capacity on flushing and CPU capacity on finding the clean cache. Only start writing dirty pages if they have cycled around the LRU twice now and STILL haven't been queued on the IO device. It's possible that the dirty pages are so sparsely distributed across different bdis, inodes, memory cgroups, that the flushers take forever to get to the ones we want reclaimed. Once we see them twice on the LRU, we know that's the quicker way to find them, so do LRU writeback. Signed-off-by: Johannes Weiner --- mm/vmscan.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 915fc658de41..df0fe0cc438e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1153,13 +1153,18 @@ static unsigned long shrink_page_list(struct list_head *page_list, if (PageDirty(page)) { /* - * Only kswapd can writeback filesystem pages to - * avoid risk of stack overflow but only writeback - * if many dirty pages have been encountered. + * Only kswapd can writeback filesystem pages + * to avoid risk of stack overflow. But avoid + * injecting inefficient single-page IO into + * flusher writeback as much as possible: only + * write pages when we've encountered many + * dirty pages, and when we've already scanned + * the rest of the LRU for clean pages and see + * the same dirty pages again (PageReclaim). */ if (page_is_file_cache(page) && - (!current_is_kswapd() || - !test_bit(PGDAT_DIRTY, &pgdat->flags))) { + (!current_is_kswapd() || !PageReclaim(page) || + !test_bit(PGDAT_DIRTY, &pgdat->flags))) { /* * Immediately reclaim when written back. * Similar in principal to deactivate_page() -- 2.11.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org