From: Miaohe Lin <linmiaohe@huawei.com>
To: Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>, Yu Zhao <yuzhao@google.com>
Cc: <akpm@linux-foundation.org>, <hannes@cmpxchg.org>,
<vbabka@suse.cz>, <axboe@kernel.dk>, <iamjoonsoo.kim@lge.com>,
<alexs@kernel.org>, <apopple@nvidia.com>, <minchan@kernel.org>,
<david@redhat.com>, <shli@fb.com>, <hillf.zj@alibaba-inc.com>,
<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/5] mm/vmscan: put the redirtied MADV_FREE pages back to anonymous LRU list
Date: Wed, 14 Jul 2021 19:36:57 +0800 [thread overview]
Message-ID: <b17caa5f-f3db-9fb0-fe1f-45510ff902c8@huawei.com> (raw)
In-Reply-To: <YO2WUx0a5go71Vhm@casper.infradead.org>
On 2021/7/13 21:34, Matthew Wilcox wrote:
> On Tue, Jul 13, 2021 at 09:13:51PM +0800, Miaohe Lin wrote:
>>>> When the MADV_FREE pages are redirtied before they could be reclaimed, the pages
>>>> should be put back to anonymous LRU list by setting SwapBacked flag, thus the
>>>> pages will be reclaimed in normal swapout way.
>>>
>>> Agreed. But the question is why this needs an explicit handling here
>>> when we already do handle this case when trying to unmap the page.
>>
>> This makes me think more. It seems even the page_ref_freeze call is guaranteed to
>> success as no one can grab the page refcnt after the page is successfully unmapped.
>
> NO! This is wrong. Every page can have its refcount speculatively raised
> (and then lowered). The two prime candidates for this are lockless GUP
> and page cache lookups, but there can be others too.
>
Many thanks for pointing this out. My overlook! Sorry!
So, it seems lockless GUP can redirty the MADV_FREE page. But is it ok to just release
a redirtied MADV_FREE pages? Because we hold the last reference here and the page will
be freed anyway...
> .
>
next prev parent reply other threads:[~2021-07-14 11:37 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-10 10:03 [PATCH 0/5] Cleanup and fixup for vmscan Miaohe Lin
2021-07-10 10:03 ` [PATCH 1/5] mm/vmscan: put the redirtied MADV_FREE pages back to anonymous LRU list Miaohe Lin
2021-07-10 23:22 ` Yu Zhao
2021-07-12 7:11 ` Miaohe Lin
2021-07-13 7:25 ` Yu Zhao
2021-07-13 13:16 ` Miaohe Lin
2021-07-12 7:22 ` Michal Hocko
2021-07-12 11:03 ` Miaohe Lin
2021-07-13 9:30 ` Michal Hocko
2021-07-13 13:13 ` Miaohe Lin
2021-07-13 13:34 ` Matthew Wilcox
2021-07-14 11:36 ` Miaohe Lin [this message]
2021-07-14 11:48 ` Matthew Wilcox
2021-07-14 19:43 ` John Hubbard
2021-07-15 11:30 ` Miaohe Lin
2021-07-16 0:01 ` John Hubbard
2021-07-16 1:53 ` Miaohe Lin
2021-07-10 10:03 ` [PATCH 2/5] mm/vmscan: remove misleading setting to sc->priority Miaohe Lin
2021-07-12 7:24 ` Michal Hocko
2021-07-12 11:10 ` Miaohe Lin
2021-07-10 10:03 ` [PATCH 3/5] mm/vmscan: remove unneeded return value of kswapd_run() Miaohe Lin
2021-07-12 7:25 ` Michal Hocko
2021-07-10 10:03 ` [PATCH 4/5] mm/vmscan: add 'else' to remove check_pending label Miaohe Lin
2021-07-12 7:26 ` Michal Hocko
2021-07-10 10:03 ` [PATCH 5/5] mm/vmscan: fix misleading comment in isolate_lru_pages() Miaohe Lin
2021-07-12 7:28 ` Michal Hocko
2021-07-12 11:16 ` Miaohe Lin
2021-07-13 9:32 ` Michal Hocko
2021-07-13 12:50 ` Miaohe Lin
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