From: Claudio Freire <klaussfreire@gmail.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: linux-kernel@vger.kernel.org,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: fadvise interferes with readahead
Date: Tue, 20 Nov 2012 12:05:02 -0300 [thread overview]
Message-ID: <CAGTBQpY-yav5G4aPSBdUmACWQbe8RR=8OnRwKHbMuuR=GBgBxw@mail.gmail.com> (raw)
In-Reply-To: <20121120145807.GB19467@localhost>
On Tue, Nov 20, 2012 at 11:58 AM, Fengguang Wu <fengguang.wu@intel.com> wrote:
>
>> But if cache hits were to simply update
>> readahead state, it would only mean that read calls behave the same
>> regardless of fadvise calls. I think that's worth pursuing.
>
> Here you are describing an alternative solution that will somehow trap
> into the readahead code even when, for example, the application is
> accessing once and again an already cached file? I'm afraid this will
> add non-trivial overheads and is less attractive than the "readahead
> on fadvise" solution.
Not for all cache hits, only those in state !PageUptodate, which are
I/O in progress, the case that hurts.
>> I ought to try to prepare a patch for this to illustrate my point. Not
>> sure I'll be able to though.
>
> I'd be glad to materialize the readahead on fadvise proposal, if there
> are no obvious negative examples/cases.
I don't expect a significant performance hit if only !PageUptodate
hits invoke readahead code. But I'm no kernel expert either.
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next prev parent reply other threads:[~2012-11-20 15:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAGTBQpaDR4+V5b1AwAVyuVLu5rkU=Wc1WeUdLu5ag=WOk5oJzQ@mail.gmail.com>
2012-11-20 8:04 ` Fengguang Wu
2012-11-20 13:20 ` Jaegeuk Hanse
2012-11-20 14:28 ` Fengguang Wu
2012-11-20 13:34 ` Claudio Freire
2012-11-20 14:58 ` Fengguang Wu
2012-11-20 15:05 ` Claudio Freire [this message]
2012-11-21 7:51 ` Jaegeuk Hanse
2012-11-21 7:57 ` Fengguang Wu
2012-11-20 14:11 ` Jaegeuk Hanse
2012-11-20 15:15 ` Fengguang Wu
2012-11-21 6:51 ` Jaegeuk Hanse
2012-11-21 7:46 ` Fengguang Wu
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