linux-kernel - Re: [RFC][PATCH] cifs: Improve use of filemap_get_folios

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Date:   Fri, 24 Feb 2023 08:22:03 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Howells <dhowells@...hat.com>
Cc:     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>,
        Matthew Wilcox <willy@...radead.org>,
        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-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] cifs: Improve use of filemap_get_folios_tag()

On Fri, Feb 24, 2023 at 7:13 AM David Howells <dhowells@...hat.com> wrote:
>
> The inefficiency derived from filemap_get_folios_tag() get a batch of
> contiguous folios in Vishal's change to afs that got copied into cifs can
> be reduced by skipping over those folios that have been passed by the start
> position rather than going through the process of locking, checking and
> trying to write them.

This patch just makes me go "Ugh".

There's something wrong with this code for it to need these games.

That  just makes me convinced that your other patch that just gets rid
of the batching entirely is the right one.

Of course, I'd be even happier if Willy is right and the code could
use the generic write_cache_pages() and avoid all of these things
entirely. I'm not clear on why cifs and afs are being so different in
the first place, and some of the differences are just odd (like that
skip count).

               Linus