From: David Rientjes <rientjes@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
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 14:46:01 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.02.1402181441360.20772@chino.kir.corp.google.com> (raw)
In-Reply-To: <20140218143838.aee7a4f0c94ab28b3b04c1e4@linux-foundation.org>
On Tue, 18 Feb 2014, Andrew Morton wrote:
> > 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.
>
Ah, ok, so 2MB is the magic value that we limit readhead to on all
architectures. 512 * 4096 is a strange way to write 2MB, but ok :)
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prev parent reply other threads:[~2014-02-18 22:46 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
2014-02-18 22:46 ` David Rientjes [this message]
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