Re: [PATCH V2] block-throttle: avoid double charge

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On 11/13/17 1:37 PM, Shaohua Li wrote:
> If a bio is throttled and splitted after throttling, the bio could be
> resubmited and enters the throttling again. This will cause part of the
> bio is charged multiple times. If the cgroup has an IO limit, the double
> charge will significantly harm the performance. The bio split becomes
> quite common after arbitrary bio size change.
> 
> To fix this, we always set the BIO_THROTTLED flag if a bio is throttled.
> If the bio is cloned/slitted, we copy the flag to new bio too to avoid
> double charge. However cloned bio could be directed to a new disk,
> keeping the flag will have problem. The observation is we always set new
> disk for the bio in this case, so we can clear the flag in
> bio_set_dev().
> 
> This issue exists a long time, arbitrary bio size change makes it worse,
> so this should go into stable at least since v4.2.
> 
> V1-> V2: Not add extra field in bio based on discussion with Tejun

Applied, thanks Shaohua.

-- 
Jens Axboe




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