From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 18 Aug 2017 09:28:25 -0700 From: Shaohua Li To: Jens Axboe CC: , Subject: Re: [PATCH] blk-throttle: ignore discard request size Message-ID: <20170818162825.GA21653@MacBook-Pro.dhcp.thefacebook.com> References: <67ffcf14c2d15622b84c60a493b590dd81a07f51.1503068984.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: List-ID: On Fri, Aug 18, 2017 at 09:35:01AM -0600, Jens Axboe wrote: > On 08/18/2017 09:13 AM, Shaohua Li wrote: > > discard request usually is very big and easily use all bandwidth budget > > of a cgroup. discard request size doesn't really mean the size of data > > written, so it doesn't make sense to account it into bandwidth budget. > > This patch ignores discard requests size. It makes sense to account > > discard request into iops budget though. > > Some (most) devices to touch media for a discard operation, but the > cost tends to be fairly constant and independent of discard size. > Would it make sense to just treat it as a constant cost? Zero > cost seems wrong. that would be hard to find the cost. Would this make sense? min_t(unsigned int, bio->bi_iter.bi_size, queue_max_sectors(q) << 9)