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Date:   Tue, 5 Jan 2021 19:39:38 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "Darrick J . Wong" <darrick.wong@oracle.com>,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH] fs: block_dev: compute nr_vecs hint for improving
 writeback bvecs allocation
Message-ID: <20210105183938.GA3878@lst.de>
References: <20210105132647.3818503-1-ming.lei@redhat.com>
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At least for iomap I think this is the wrong approach.  Between the
iomap and writeback_control we know the maximum size of the writeback
request and can just use that.  Take a look at what iomap_readpage_actor
does on the read size, something similar taking the wbc into account
can be done on the writeback side.