linux-kernel - Re: [PATCH v1 12/15] fs/direct-io: keep track of wether a page is coming from GUP or not

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Message-ID: <20190411231443.GD1695@dread.disaster.area>
Date:   Fri, 12 Apr 2019 09:14:43 +1000
From:   Dave Chinner <david@...morbit.com>
To:     jglisse@...hat.com
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-mm@...ck.org,
        John Hubbard <jhubbard@...dia.com>, Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Ming Lei <ming.lei@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Matthew Wilcox <willy@...radead.org>,
        Ernesto A . Fernández 
        <ernesto.mnd.fernandez@...il.com>, Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH v1 12/15] fs/direct-io: keep track of wether a page is
 coming from GUP or not

On Thu, Apr 11, 2019 at 05:08:31PM -0400, jglisse@...hat.com wrote:
> From: Jérôme Glisse <jglisse@...hat.com>
> 
> We want to keep track of how we got a reference on page when doing DIO,
> ie wether the page was reference through GUP (get_user_page*) or not.
> For that this patch rework the way page reference is taken and handed
> over between DIO code and BIO. Instead of taking a reference for page
> that have been successfuly added to a BIO we just steal the reference
> we have when we lookup the page (either through GUP or for ZERO_PAGE).
> 
> So this patch keep track of wether the reference has been stolen by the
> BIO or not. This avoids a bunch of get_page()/put_page() so this limit
> the number of atomic operations.

Is the asme set of changes appropriate for the fs/iomap.c direct IO
path (i.e. XFS)?

-Dave.
-- 
Dave Chinner
david@...morbit.com