linux-kernel - Re: [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG

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Date:   Mon, 22 Mar 2021 10:56:26 +0000
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Alexander Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...hat.com>,
        David Wysochanski <dwysocha@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG_fscache

Matthew Wilcox <willy@...radead.org> wrote:

> That also brings up that there is no set_page_private_2().  I think
> that's OK -- you only set PageFsCache() immediately after reading the
> page from the server.  But I feel this "unlock_page_private_2" is actually
> "clear_page_private_2" -- ie it's equivalent to writeback, not to lock.

How about I do the following:

 (1) Add set_page_private_2() or mark_page_private_2() to set the PG_fscache_2
     bit.  It could take a ref on the page here.

 (2) Rename unlock_page_private_2() to end_page_private_2().  It could drop
     the ref on the page here, but that then means I can't use
     pagevec_release().

 (3) Add wait_on_page_private_2() an analogue of wait_on_page_writeback()
     rather than wait_on_page_locked().

 (4) Provide fscache synonyms of the above.

David