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Date: Mon, 14 Aug 2017 17:48:37 +0900
From: Minchan Kim <minchan@kernel.org>
Subject: Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has
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To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>, Dave Chinner <david@fromorbit.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Matthew Wilcox <willy@infradead.org>, linux-mm <linux-mm@kvack.org>, kernel-team <kernel-team@lge.com>, seungho1.park@lge.com, "karam . lee" <karam.lee@lge.com>
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Hi Christoph,

On Fri, Aug 11, 2017 at 12:46:15PM +0200, Christoph Hellwig wrote:
> On Wed, Aug 09, 2017 at 08:06:24PM -0700, Dan Williams wrote:
> > I like it, but do you think we should switch to sbvec[<constant>] to
> > preclude pathological cases where nr_pages is large?
> 
> Yes, please.

Still, I don't understand how sbvec[nr_pages] with on-stack bio in
do_mpage_readpage can help the performance.

IIUC, do_mpage_readpage works with page-base. IOW, it passes just one
page, not multiple pages so if we use on-stack bio, we just add *a page*
via bio_add_page and submit the bio before the function returning.

So, rather than sbvec[1], why de we need sbvec[nr_pages]?

Please, let me open my eyes. :)

Thanks.
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