linux-kernel - Re: [RFC PATCH V4] mm readahead: Fix readahead fail for no local memory and limit readahead pages

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Message-ID: <52D7C130.3010306@linux.vnet.ibm.com>
Date:	Thu, 16 Jan 2014 16:53:28 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus <torvalds@...ux-foundation.org>
CC:	Jan Kara <jack@...e.cz>, Fengguang Wu <fengguang.wu@...el.com>,
	David Cohen <david.a.cohen@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Damien Ramonda <damien.ramonda@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH V4] mm readahead: Fix readahead fail for no local
 memory and limit readahead pages

On 01/10/2014 03:22 PM, Jan Kara wrote:
> On Fri 10-01-14 09:36:56, Jan Kara wrote:
>> On Fri 10-01-14 00:54:50, Raghavendra K T wrote:
>>> We limit the number of readahead pages to 4k.
>>>
>>> max_sane_readahead returns zero on the cpu having no local memory
>>> node. Fix that by returning a sanitized number of pages viz.,
>>> minimum of (requested pages, 4k, number of local free pages)
>>>
>>> Result:
>>> fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile
>>> 32GB* 4G RAM  numa machine ( 12 iterations) yielded
>>>
>>> kernel       Avg        Stddev
>>> base         7.264      0.56%
>>> patched      7.285      1.14%
>>    OK, looks good to me. You can add:
>> Reviewed-by: Jan Kara <jack@...e.cz>
>    Hum, while doing some other work I've realized there may be still a
> problem hiding with the 16 MB limitation. E.g. the dynamic linker is
> doing MADV_WILLNEED on the shared libraries. If the library (or executable)
> is larger than 16 MB, then it may cause performance problems since access
> is random in nature and we don't really know which part of the file do we
> need first.
>
> I'm not sure what others think about this but I'm now more inclined to a
> bit more careful and introduce the 16 MB limit only for the NUMA case. I.e.
> something like:
>

Hi Linus, Andrew,

Could you please let us know your suggestion or comment?

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