linux-kernel - Re: [RFC PATCH 0/7] mm: Make more use of readahead

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Message-ID: <423539.1598989454@warthog.procyon.org.uk>
Date:   Tue, 01 Sep 2020 20:44:14 +0100
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/7] mm: Make more use of readahead_control

Matthew Wilcox <willy@...radead.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