Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley
        Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United
        Kingdom.
        Registered in England and Wales under Company Registration No. 3798903
From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20200901164827.GQ14765@casper.infradead.org>
References: <20200901164827.GQ14765@casper.infradead.org> <159897769535.405783.17587409235571100774.stgit@warthog.procyon.org.uk>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     dhowells@redhat.com, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/7] mm: Make more use of readahead_control
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <423538.1598989454.1@warthog.procyon.org.uk>
Date:   Tue, 01 Sep 2020 20:44:14 +0100
Message-ID: <423539.1598989454@warthog.procyon.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Matthew Wilcox <willy@infradead.org> wrote:

> > Note that I've been
> > passing the number of pages to read in rac->_nr_pages, and then saving it
> > and changing it certain points, e.g. page_cache_readahead_unbounded().
> 
> I do not like this.  You're essentially mutating the meaning of _nr_pages
> as the ractl moves down the stack, and that's going to lead to bugs.
> I'd keep it as a separate argument.

The meaning isn't specified in linux/pagemap.h.  Can you adjust the comments
on the struct and on readahead_count() to make it more clear what the value
represents?

Thanks,
David