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

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Message-ID: <CAHk-=wgpjrdcs_aFvdHdH6TpOsOmN9S5rXDqCZTB8WqXsZH8Qw@mail.gmail.com>
Date:   Fri, 24 Feb 2023 12:16:49 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.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 12:14 PM David Howells <dhowells@...hat.com> wrote:
>
> Then why do we have to wait for PG_writeback to complete?

At least for PG_writeback, it's about "the _previous_ dirty write is
still under way, but - since PG_dirty is set again - the page has been
dirtied since".

So we have to start _another_ writeback, because while the current
writeback *might* have written the updated data, that is not at all
certain or clear.

I'm not sure what the fscache rules are.

                Linus