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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Josef Bacik <josef@toxicpanda.com>
Cc: Matthew Wilcox <willy@infradead.org>, Chris Mason <clm@fb.com>,
	David Sterba <dsterba@suse.com>,
	David Howells <dhowells@redhat.com>,
	Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	Christoph Hellwig <hch@lst.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Linux-MM <linux-mm@kvack.org>,
	linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
	"open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>,
	CIFS <linux-cifs@vger.kernel.org>,
	ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG_fscache
Date: Tue, 16 Mar 2021 19:35:17 -0700	[thread overview]
Message-ID: <CAHk-=whWoJhGeMn85LOh9FX-5d2-Upzmv1m2ZmYxvD31TKpUTA@mail.gmail.com> (raw)
In-Reply-To: <887b9eb7-2764-3659-d0bf-6a034a031618@toxicpanda.com>

On Tue, Mar 16, 2021 at 7:12 PM Josef Bacik <josef@toxicpanda.com> wrote:
>
>
> Yeah it's just a flag, we use it to tell that the page is part of a range that
> has been allocated for IO.  The lifetime of the page is independent of the page,
> but is generally either dirty or under writeback, so either it goes through
> truncate and we clear PagePrivate2 there, or it actually goes through IO and is
> cleared before we drop the page in our endio.

Ok, that's what it looked like from my very limited "looking at a
couple of grep cases", but I didn't go any further than that.

> We _always_ have PG_private set on the page as long as we own it, and
> PG_private_2 is only set in this IO related context, so we're safe
> there because of the rules around PG_dirty/PG_writeback. We don't need
> it to have an extra ref for it being set.

Perfect. That means that at least as far as btrfs is concerned, we
could trivially remove PG_private_2 from that page_has_private() math
- you'd always see the same result anyway, exactly because you have
PG_private set.

And as far as I can tell, fscache doesn't want that PG_private_2 bit
to interact with the random VM lifetime or migration rules either, and
should rely entirely on the page count. David?

There's actually a fair number of page_has_private() users, so we'd
better make sure that's the case. But it's simplified by this but
really only being used by btrfs (which doesn't care) and fscache, so
this cleanup would basically be entirely up to the whole fscache
series.

Hmm? Objections?

            Linus

  reply	other threads:[~2021-03-17  2:36 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-10 16:54 [PATCH v4 00/28] Network fs helper library & fscache kiocb API David Howells
2021-03-10 16:54 ` [PATCH v4 01/28] iov_iter: Add ITER_XARRAY David Howells
2021-03-10 16:54 ` [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG_fscache David Howells
2021-03-16 19:07   ` Matthew Wilcox
2021-03-17  0:43     ` Linus Torvalds
2021-03-17  0:43       ` Linus Torvalds
2021-03-17  2:12       ` Josef Bacik
2021-03-17  2:35         ` Linus Torvalds [this message]
2021-03-17  2:35           ` Linus Torvalds
2021-03-17  9:04         ` David Howells
2021-03-17 10:53         ` David Howells
2021-03-16 20:38   ` David Howells
2021-03-16 23:32     ` Matthew Wilcox
2021-03-21 10:53   ` Matthew Wilcox
2021-03-22 10:56   ` David Howells
2021-03-23 13:17   ` David Howells
2021-03-23 13:51     ` Matthew Wilcox
2021-03-23 14:16     ` David Howells
2021-03-23 22:06     ` David Howells
2021-03-23 22:06       ` David Howells
2021-03-10 16:55 ` [PATCH v4 03/28] mm: Implement readahead_control pageset expansion David Howells
2021-03-10 16:55 ` [PATCH v4 04/28] netfs: Make a netfs helper module David Howells
2021-03-10 16:55 ` [PATCH v4 05/28] netfs: Documentation for helper library David Howells
2021-03-10 16:55 ` [PATCH v4 06/28] netfs, mm: Move PG_fscache helper funcs to linux/netfs.h David Howells
2021-03-10 16:56 ` [PATCH v4 07/28] netfs, mm: Add unlock_page_fscache() and wait_on_page_fscache() David Howells
2021-03-10 16:56 ` [PATCH v4 08/28] netfs: Provide readahead and readpage netfs helpers David Howells
2021-03-21  1:42   ` Matthew Wilcox
2021-03-22 17:13   ` David Howells
2021-03-10 16:56 ` [PATCH v4 09/28] netfs: Add tracepoints David Howells
2021-03-10 16:56 ` [PATCH v4 10/28] netfs: Gather stats David Howells
2021-03-10 16:56 ` [PATCH v4 11/28] netfs: Add write_begin helper David Howells
2021-03-10 16:57 ` [PATCH v4 12/28] netfs: Define an interface to talk to a cache David Howells
2021-03-10 16:57 ` [PATCH v4 13/28] netfs: Hold a ref on a page when PG_private_2 is set David Howells
2021-03-10 16:57 ` [PATCH v4 14/28] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-03-10 16:57 ` [PATCH v4 15/28] afs: Disable use of the fscache I/O routines David Howells
2021-03-10 16:58 ` [PATCH v4 16/28] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-03-10 16:58 ` [PATCH v4 17/28] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-03-10 16:58 ` [PATCH v4 18/28] afs: Move key to afs_read struct David Howells
2021-03-10 16:58 ` [PATCH v4 19/28] afs: Don't truncate iter during data fetch David Howells
2021-03-10 16:58 ` [PATCH v4 20/28] afs: Log remote unmarshalling errors David Howells
2021-03-10 16:59 ` [PATCH v4 21/28] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-03-10 16:59 ` [PATCH v4 22/28] afs: Use ITER_XARRAY for writing David Howells
2021-03-10 16:59 ` [PATCH v4 23/28] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-03-10 16:59 ` [PATCH v4 24/28] afs: Extract writeback extension into its own function David Howells
2021-03-10 16:59 ` [PATCH v4 25/28] afs: Prepare for use of THPs David Howells
2021-03-10 17:00 ` [PATCH v4 26/28] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-03-10 17:00 ` [PATCH v4 27/28] afs: Use new fscache read helper API David Howells
2021-03-10 17:00 ` [PATCH v4 28/28] afs: Use the fscache_write_begin() helper David Howells
2021-03-16 11:34 ` [PATCH v4 08/28] netfs: Provide readahead and readpage netfs helpers David Howells

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