linux-kernel - Re: [PATCH 5/6] f2fs: add a kernel thread to issue discard commands asynchronously

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Message-ID: <20170116173220.GA2199@infradead.org>
Date:   Mon, 16 Jan 2017 09:32:20 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, axboe@...nel.dk
Subject: Re: [PATCH 5/6] f2fs: add a kernel thread to issue discard commands
 asynchronously

On Fri, Jan 13, 2017 at 11:12:11AM -0800, Jaegeuk Kim wrote:
> Previously, I've done to issue discard bios asynchronously. But the problem that
> I've got is that was not enough. When testing nvme SSD with noop IO scheduler,
> submit_bio() was blocked at every 8 async discard bios, resulting in very slow
> checkpoint process which blocks most of other FS operations.

Where does it block?  Are you running out of request?  What driver is
this on top of?