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bug#9500: [PATCH]: use posix_fallocate where supported

From: Pádraig Brady
Subject: bug#9500: [PATCH]: use posix_fallocate where supported
Date: Tue, 29 Nov 2011 14:13:27 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0

On 11/29/2011 01:22 PM, Jim Meyering wrote:
> Pádraig Brady wrote:
>> On 11/25/2011 10:59 AM, Pádraig Brady wrote:
>>> On 11/25/2011 10:13 AM, Pádraig Brady wrote:
>>>> Hmm, one of your points above got me thinking.
>>>> Might fallocate() fail to allocate an extent with ENOSPC,
>>>> but there could be fragmented space available to write()?
>>>> That would scupper benefit (2) above :(
>>>> I'll ask address@hidden
>>> And the response from there is that fallocate() will
>>> check the free blocks first, and then try to allocate
>>> as a contiguous extent, but that part is not guaranteed.
>>> So we still get benefit (2).
>> However that thread has continued, and it
>> was mentioned that benefit (1) might actually
>> be detrimental, at least for small files.
>> http://thread.gmane.org/gmane.linux.file-systems/59092
> Sigh, indeed.
> Do you think it's even worth an option, now?

Having an option to enable is much less interesting.
One might auto-enable it for files > 16MB or something.
I'm reserving judgement until I understand the issues better.


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