[Gluster-devel] Changing the relative order of read-ahead and open-behind

[Pranith Kumar Karampuri]

On Mon, Jul 24, 2017 at 5:11 PM, Raghavendra G <raghavendra at gluster.com>
wrote:

>
>
> On Fri, Jul 21, 2017 at 6:39 PM, Vijay Bellur <vbellur at redhat.com> wrote:
>
>>
>> On Fri, Jul 21, 2017 at 3:26 AM, Raghavendra Gowdappa <
>> rgowdapp at redhat.com> wrote:
>>
>>> Hi all,
>>>
>>> We've a bug [1], due to which read-ahead is completely disabled when the
>>> workload is read-only. One of the easy fix was to make read-ahead as an
>>> ancestor of open-behind in xlator graph (Currently its a descendant). A
>>> patch has been sent out by Rafi to do the same. As noted in one of the
>>> comments, one flip side of this solution is that small files (which are
>>> eligible to be cached by quick read) are cached twice - once each in
>>> read-ahead and quick-read - wasting up precious memory. However, there are
>>> no other simpler solutions for this issue. If you've concerns on the
>>> approach followed by [2] or have other suggestions please voice them out.
>>> Otherwise, I am planning to merge [2] for lack of better alternatives.
>>>
>>
>>
>> Since the maximum size of files cached by quick-read is 64KB, can we have
>> read-ahead kick in for offsets greater than 64KB?
>>
>
> I got your point. We can enable read-ahead only for files whose size is
> greater than the size eligible for caching quick-read. IOW, read-ahead gets
> disabled if file size is less than 64KB. Thanks for the suggestion.
>

I added a comment on the patch to move the xlators in reverse to the way
the patch is currently doing. Milind I think implemented it. Will that lead
to any problem?


>
>
>>
>> Thanks,
>> Vijay
>>
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>>
>
>
>
> --
> Raghavendra G
>
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>



-- 
Pranith
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