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

[Raghavendra G]

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.


>
> Thanks,
> Vijay
>
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-- 
Raghavendra G
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