From: Andrea Arcangeli <aarcange@redhat.com>
To: "Figo.zhang" <figo1802@gmail.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
mel@csn.ul.ie, "linux-mm@kvack.org" <linux-mm@kvack.org>,
kamezawa.hiroyu@jp.fujisu.com, minchan.kim@gmail.com,
Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH]mm/compation.c: checking page in lru twice
Date: Fri, 6 May 2011 20:21:51 +0200 [thread overview]
Message-ID: <20110506182151.GG6330@random.random> (raw)
In-Reply-To: <1304681575.15473.4.camel@figo-desktop>
On Fri, May 06, 2011 at 07:32:46PM +0800, Figo.zhang wrote:
>
> in isolate_migratepages() have check page in LRU twice, the next one
> at _isolate_lru_page().
hugetlbfs or any other compound page won't have PageLRU set and they
may go away from under us leading to compound_order not being reliable
if we remove the PageLRU check before compound_order. So we need to
verify the page is in LRU before running compound_order safely. And if
we hold the lru_lock, the page won't be isolated under us, and we know
it's not going to get splitted either.
We might use compound_trans_order but that's only reliable if run on
the head page so it's not so reliable, and so far it's only used by
memory-failure to "diminish" the risk of races in reading the compound
order, but it's not the best having to use compound_trans_order (and
memory-failure remains unsafe w.r.t to hugetlbfs being released during
hwpoisoning, so compound_trans_order might have to be improved for
it).
WARNING: multiple messages have this Message-ID (diff)
From: Andrea Arcangeli <aarcange@redhat.com>
To: "Figo.zhang" <figo1802@gmail.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
mel@csn.ul.ie, "linux-mm@kvack.org" <linux-mm@kvack.org>,
kamezawa.hiroyu@jp.fujisu.com, minchan.kim@gmail.com,
Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH]mm/compation.c: checking page in lru twice
Date: Fri, 6 May 2011 20:21:51 +0200 [thread overview]
Message-ID: <20110506182151.GG6330@random.random> (raw)
In-Reply-To: <1304681575.15473.4.camel@figo-desktop>
On Fri, May 06, 2011 at 07:32:46PM +0800, Figo.zhang wrote:
>
> in isolate_migratepages() have check page in LRU twice, the next one
> at _isolate_lru_page().
hugetlbfs or any other compound page won't have PageLRU set and they
may go away from under us leading to compound_order not being reliable
if we remove the PageLRU check before compound_order. So we need to
verify the page is in LRU before running compound_order safely. And if
we hold the lru_lock, the page won't be isolated under us, and we know
it's not going to get splitted either.
We might use compound_trans_order but that's only reliable if run on
the head page so it's not so reliable, and so far it's only used by
memory-failure to "diminish" the risk of races in reading the compound
order, but it's not the best having to use compound_trans_order (and
memory-failure remains unsafe w.r.t to hugetlbfs being released during
hwpoisoning, so compound_trans_order might have to be improved for
it).
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next prev parent reply other threads:[~2011-05-06 18:22 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-06 11:32 [PATCH]mm/compation.c: checking page in lru twice Figo.zhang
2011-05-06 11:32 ` Figo.zhang
2011-05-06 13:09 ` Mel Gorman
2011-05-06 13:09 ` Mel Gorman
2011-05-06 18:26 ` Andrea Arcangeli
2011-05-06 18:26 ` Andrea Arcangeli
2011-05-06 18:21 ` Andrea Arcangeli [this message]
2011-05-06 18:21 ` Andrea Arcangeli
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