From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f182.google.com (mail-pd0-f182.google.com [209.85.192.182]) by kanga.kvack.org (Postfix) with ESMTP id D39476B0032 for ; Wed, 11 Feb 2015 16:09:07 -0500 (EST) Received: by pdjg10 with SMTP id g10so6858836pdj.1 for ; Wed, 11 Feb 2015 13:09:07 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id bz1si2194619pbb.244.2015.02.11.13.09.06 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Feb 2015 13:09:06 -0800 (PST) Date: Wed, 11 Feb 2015 13:09:05 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: fix negative nr_isolated counts Message-Id: <20150211130905.4b0d1809b0689ffd6e83d851@linux-foundation.org> In-Reply-To: References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Vlastimil Babka , linux-mm@kvack.org, Joonsoo Kim On Tue, 10 Feb 2015 23:06:09 -0800 (PST) Hugh Dickins wrote: > The vmstat interfaces are good at hiding negative counts (at least > when CONFIG_SMP); but if you peer behind the curtain, you find that > nr_isolated_anon and nr_isolated_file soon go negative, and grow ever > more negative: so they can absorb larger and larger numbers of isolated > pages, yet still appear to be zero. > > I'm happy to avoid a congestion_wait() when too_many_isolated() myself; > but I guess it's there for a good reason, in which case we ought to get > too_many_isolated() working again. > > The imbalance comes from isolate_migratepages()'s ISOLATE_ABORT case: > putback_movable_pages() decrements the NR_ISOLATED counts, but we forgot > to call acct_isolated() to increment them. So if I'm understanding this correctly, shrink_inactive_list()'s call to congestion_wait() basically never happens? If so I'm pretty reluctant to merge this up until it has had plenty of careful testing - there's a decent chance that it will make the kernel behave worse. > Fixes: edc2ca612496 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()") > Signed-off-by: Hugh Dickins > Cc: stable@vger.kernel.org # v3.18+ And why -stable? What user-visible problem is the bug causing? -- 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