linux-kernel - Re: [RFC][PATCH] cifs: Fix cifs_writepages

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Message-ID: <Y/jhwuTCaOgOTLp2@casper.infradead.org>
Date:   Fri, 24 Feb 2023 16:11:46 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Steve French <stfrench@...rosoft.com>,
        Vishal Moola <vishal.moola@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Paulo Alcantara <pc@....nz>,
        Huang Ying <ying.huang@...el.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Xin Hao <xhao@...ux.alibaba.com>, linux-mm@...ck.org,
        mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] cifs: Fix cifs_writepages_region()

On Fri, Feb 24, 2023 at 02:31:15PM +0000, David Howells wrote:
> Here's the simplest fix for cifs_writepages_region() that gets it to work.
> 
> Fix the cifs_writepages_region() to just skip over members of the batch that
> have been cleaned up rather than retrying them.  I'm not entirely sure why it
> fixes it, though.  It's also not the most efficient as, in the common case,
> this is going to happen a lot because cifs_extend_writeback() is going to
> clean up the contiguous pages in the batch - and then this skip will occur for
> those.

Why are you doing it this way?  What's wrong with using
write_cache_pages() to push all the contiguous dirty folios into a single
I/O object, submitting it when the folios turn out not to be contiguous,
or when we run out of a batch?

You've written an awful lot of code here and it's a different model from
every other filesystem.  Why is it better?