From: Andrew Morton <akpm@linux-foundation.org>
To: David Rientjes <rientjes@google.com>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
Fengguang Wu <fengguang.wu@intel.com>,
David Cohen <david.a.cohen@linux.intel.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Damien Ramonda <damien.ramonda@intel.com>,
Jan Kara <jack@suse.cz>, Linus <torvalds@linux-foundation.org>,
nacc@linux.vnet.ibm.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V6 ] mm readahead: Fix readahead fail for memoryless cpu and limit readahead pages
Date: Tue, 18 Feb 2014 14:38:38 -0800 [thread overview]
Message-ID: <20140218143838.aee7a4f0c94ab28b3b04c1e4@linux-foundation.org> (raw)
In-Reply-To: <alpine.DEB.2.02.1402181421590.20772@chino.kir.corp.google.com>
On Tue, 18 Feb 2014 14:23:44 -0800 (PST) David Rientjes <rientjes@google.com> wrote:
> On Tue, 18 Feb 2014, Raghavendra K T wrote:
>
> > Currently max_sane_readahead() returns zero on the cpu having no local memory node
> > which leads to readahead failure. Fix the readahead failure by returning
> > minimum of (requested pages, 512). Users running application on a memory-less cpu
> > which needs readahead such as streaming application see considerable boost in the
> > performance.
> >
> > Result:
> > fadvise experiment with FADV_WILLNEED on a PPC machine having memoryless CPU
> > with 1GB testfile ( 12 iterations) yielded around 46.66% improvement.
> >
> > fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile
> > 32GB* 4G RAM numa machine ( 12 iterations) showed no impact on the normal
> > NUMA cases w/ patch.
> >
> > Kernel Avg Stddev
> > base 7.4975 3.92%
> > patched 7.4174 3.26%
> >
> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > [Andrew: making return value PAGE_SIZE independent]
> > Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
>
> So this replaces
> mm-readaheadc-fix-readahead-fail-for-no-local-memory-and-limit-readahead-pages.patch
> in -mm correct?
yup.
> > Changes in V6:
> > - Just limit the readahead to 2MB on 4k pages system as suggested by Linus.
> > and make it independent of PAGE_SIZE.
> >
>
> I'm not sure I understand why we want to be independent of PAGE_SIZE since
> we're still relying on PAGE_CACHE_SIZE. Don't you mean to do
>
> #define MAX_READAHEAD ((512*PAGE_SIZE)/PAGE_CACHE_SIZE)
MAX_READAHEAD is in units of "pages".
This:
+#define MAX_READAHEAD ((512*4096)/PAGE_CACHE_SIZE)
means "two megabytes", and is implemented in a way to ensure that
MAX_READAHEAD=2mb on 4k pagesize as well as on 64k pagesize. Because
we don't want variations in PAGE_SIZE to cause alterations in readahead
behavior.
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next prev parent reply other threads:[~2014-02-18 22:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-18 7:25 Raghavendra K T
2014-02-18 9:49 ` Jan Kara
2014-02-18 12:04 ` Raghavendra K T
2014-02-18 12:04 ` Jan Kara
2014-03-17 2:07 ` Madper Xie
2014-03-18 7:13 ` Raghavendra K T
2014-02-18 22:23 ` David Rientjes
2014-02-18 22:38 ` Andrew Morton [this message]
2014-02-18 22:46 ` David Rientjes
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