From: Michal Hocko <mhocko@kernel.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Tim Chen <tim.c.chen@linux.intel.com>,
Minchan Kim <minchan@kernel.org>,
stable@vger.kernel.org, Christian Kujau <lists@nerdbynature.de>
Subject: Re: [PATCH -mm] mm, swap: Fix false error message in __swp_swapcount()
Date: Tue, 24 Oct 2017 17:30:37 +0200 [thread overview]
Message-ID: <20171024153037.gjemriarubzoqai5@dhcp22.suse.cz> (raw)
In-Reply-To: <87vaj4poff.fsf@yhuang-dev.intel.com>
On Tue 24-10-17 23:15:32, Huang, Ying wrote:
> Hi, Michal,
>
> Michal Hocko <mhocko@kernel.org> writes:
>
> > On Tue 24-10-17 10:47:00, Huang, Ying wrote:
> >> From: Ying Huang <ying.huang@intel.com>
> >>
> >> __swp_swapcount() is used in __read_swap_cache_async(). Where the
> >> invalid swap entry (offset > max) may be supplied during swap
> >> readahead. But __swp_swapcount() will print error message for these
> >> expected invalid swap entry as below, which will make the users
> >> confusing.
> > ^^
> > confused... And I have to admit this changelog has left me confused as
> > well. What is an invalid swap entry in the readahead? Ohh, let me
> > re-real Fixes: commit. It didn't really help "We can avoid needlessly
> > allocating page for swap slots that are not used by anyone. No pages
> > have to be read in for these slots."
> >
> > Could you be more specific about when and how this happens please?
>
> Sorry for confusing.
>
> When page fault occurs for a swap entry, the original swap readahead
> (not new VMA base swap readahead) may readahead several swap entries
> after the fault swap entry. The readahead algorithm calculates some of
> the swap entries to readahead via increasing the offset of the fault
> swap entry without checking whether they are beyond the end of the swap
> device and it rely on the __swp_swapcount() and swapcache_prepare() to
> check it. Although __swp_swapcount() checks for the swap entry passed
> in, it will complain with error message for the expected invalid swap
> entry. This makes the end user confusing.
>
> Is this a little clearer.
yes, this makes more sense (modulo the same typo ;)). Can you make this
information into the changelog please? Thanks.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-10-24 15:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-24 2:47 Huang, Ying
2017-10-24 8:38 ` Michal Hocko
2017-10-24 15:15 ` Huang, Ying
2017-10-24 15:30 ` Michal Hocko [this message]
2017-10-24 15:34 ` Huang, Ying
2017-10-24 20:17 ` Minchan Kim
2017-10-25 2:32 ` Huang, Ying
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