[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20190814154929.f050d937f2bd2c4d80c7f772@linux-foundation.org>
Date: Wed, 14 Aug 2019 15:49:29 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: David Rientjes <rientjes@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [patch] mm, page_alloc: move_freepages should not examine
struct page of reserved memory
On Tue, 13 Aug 2019 16:31:35 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:
> > > Move the debug checks to after verifying PageBuddy is true. This isolates
> > > the scope of the checks to only be for buddy pages which are on the zone's
> > > freelist which move_freepages_block() is operating on. In this case, an
> > > incorrect node or zone is a bug worthy of being warned about (and the
> > > examination of struct page is acceptable bcause this memory is not
> > > reserved).
> >
> > I'm thinking Fixes:907ec5fca3dc and Cc:stable? But 907ec5fca3dc is
> > almost a year old, so you were doing something special to trigger this?
> >
>
> We noticed it almost immediately after bringing 907ec5fca3dc in on
> CONFIG_DEBUG_VM builds. It depends on finding specific free pages in the
> per-zone free area where the math in move_freepages() will bring the start
> or end pfn into reserved memory and wanting to claim that entire pageblock
> as a new migratetype. So the path will be rare, require CONFIG_DEBUG_VM,
> and require fallback to a different migratetype.
>
> Some struct pages were already zeroed from reserve pages before
> 907ec5fca3c so it theoretically could trigger before this commit. I think
> it's rare enough under a config option that most people don't run that
> others may not have noticed. I wouldn't argue against a stable tag and
> the backport should be easy enough, but probably wouldn't single out a
> commit that this is fixing.
OK, thanks. I added the above two paragraphs to the changelog and
removed the Fixes:
Hopefully Mel will be able to review this for us.
Powered by blists - more mailing lists