Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 30 Oct 2019 15:01:44 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Philippe Liard <pliard@google.com>
Cc:     phillip@squashfs.org.uk, hch@lst.de, linux-kernel@vger.kernel.org,
        groeck@chromium.org
Subject: Re: [PATCH] squashfs: Migrate from ll_rw_block usage to BIO
Message-ID: <20191030140144.GA14098@lst.de>
References: <20191029074939.GA18999@lst.de> <20191030011954.60006-1-pliard@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20191030011954.60006-1-pliard@google.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Oct 30, 2019 at 10:19:54AM +0900, Philippe Liard wrote:
> > What access do you need to synchronize?  If you read data into the
> > page cache the page lock provides all synchronization needed.  If
> > you just read into decrompression buffers there probably is no need
> > for synchronization at all as each buffer is only accessed by one
> > thread at a time.
> My main concern here was waiting for the BIO request to complete but
> submit_bio_wait() that you pointed out below should address that.

Note that if you are doing multiple bios for a single request using
submit_bio_wait might not be optimal.  In that case you probably want
a refcount and only complete when all of them are done, but by looking
at submit_bio_wait should get an idea how that works.  Alternatively look
at others users, e.g. __blkdev_direct_IO in fs/block_dev.c that already
support multiple bios.