Message-ID: <4E08346F.3070203@jp.fujitsu.com>
Date: Mon, 27 Jun 2011 16:42:39 +0900
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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To: andrea@betterlinux.com
CC: akpm@linux-foundation.org, minchan.kim@gmail.com, riel@redhat.com,
        peterz@infradead.org, hannes@cmpxchg.org,
        kamezawa.hiroyu@jp.fujitsu.com, aarcange@redhat.com, hughd@google.com,
        jamesjer@betterlinux.com, marcus@bluehost.com, matt@bluehost.com,
        tytso@mit.edu, shaohua.li@intel.com, P@draigBrady.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 0/2] fadvise: support POSIX_FADV_NOREUSE
References: <1308923350-7932-1-git-send-email-andrea@betterlinux.com> <4E07F349.2040900@jp.fujitsu.com> <20110627071139.GC1247@thinkpad>
In-Reply-To: <20110627071139.GC1247@thinkpad>
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>>>  POSIX_FADV_DONTNEED = drop page cache if possible
>>>  POSIX_FADV_NOREUSE = reduce page cache eligibility
>>
>> Eeek.
>>
>> Your POSIX_FADV_NOREUSE is very different from POSIX definition.
>> POSIX says,
>>
>>        POSIX_FADV_NOREUSE
>>               Specifies that the application expects to access the specified data once  and  then
>>               not reuse it thereafter.
>>
>> IfI understand correctly, it designed for calling _before_ data access
>> and to be expected may prevent lru activation. But your NORESE is designed
>> for calling _after_ data access. Big difference might makes a chance of
>> portability issue.
> 
> You're right. NOREUSE is designed to implement drop behind policy.
> 
> I'll post a new patch that will plug this logic in DONTNEED (like the
> presious version), but without breaking the old /proc/sys/vm/drop_caches
> behavior.

Great!

thanks.


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