linux-kernel - Re: [PATCH v8 03/10] mm: Provide a helper to drop a pin/ref on a page

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Message-ID: <874546.1674571293@warthog.procyon.org.uk>
Date:   Tue, 24 Jan 2023 14:41:33 +0000
From:   David Howells <dhowells@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-mm@...ck.org
Subject: Re: [PATCH v8 03/10] mm: Provide a helper to drop a pin/ref on a page

David Hildenbrand <david@...hat.com> wrote:

> > Provide a helper in the get_user_pages code to drop a pin or a ref on a
> > page based on being given FOLL_GET or FOLL_PIN in its flags argument or do
> > nothing if neither is set.
> 
> Does the FOLL_GET part still apply to this patch set?

Yes.  Christoph insisted that the bio conversion patch be split up.  That
means there's an interval where you can get FOLL_GET from that.  However,
since Jason wants to hide FOLL_PUT, this is going to have to be removed and
the switching done in the bio code for the bio case (until that reduces to
just pinning) and the skbuff cleanup code (when that is eventually done - that
will have the possibility of skbuffs comprising a mix of ref'd, pinned and
unpinned data, albeit in separate fragments; I've posted patches that
illustrate this[1]).

David

https://lore.kernel.org/all/167391047703.2311931.8115712773222260073.stgit@warthog.procyon.org.uk/ [1] Patches 33-34