MIME-Version: 1.0
References: <Y/jhwuTCaOgOTLp2@casper.infradead.org> <2134430.1677240738@warthog.procyon.org.uk>
 <2009825.1677229488@warthog.procyon.org.uk> <CAHk-=whAAOVBrzwb2uMjCmdRrtudGesYj0tuqdUgi8X_gbw1jw@mail.gmail.com>
 <20230220135225.91b0f28344c01d5306c31230@linux-foundation.org>
 <2213409.1677249075@warthog.procyon.org.uk> <2385089.1677258941@warthog.procyon.org.uk>
 <Y/kFnhUM5hjWM2Ae@casper.infradead.org> <2390711.1677269637@warthog.procyon.org.uk>
In-Reply-To: <2390711.1677269637@warthog.procyon.org.uk>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 24 Feb 2023 12:16:49 -0800
Message-ID: <CAHk-=wgpjrdcs_aFvdHdH6TpOsOmN9S5rXDqCZTB8WqXsZH8Qw@mail.gmail.com>
Subject: Re: [RFC][PATCH] cifs: Fix cifs_writepages_region()
To:     David Howells <dhowells@redhat.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Steve French <stfrench@microsoft.com>,
        Vishal Moola <vishal.moola@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jan Kara <jack@suse.cz>, Paulo Alcantara <pc@cjr.nz>,
        Huang Ying <ying.huang@intel.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Xin Hao <xhao@linux.alibaba.com>, linux-mm@kvack.org,
        mm-commits@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Feb 24, 2023 at 12:14 PM David Howells <dhowells@redhat.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