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From: David Howells <dhowells@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: dhowells@redhat.com, Matthew Wilcox <willy@infradead.org>,
	Jeff Layton <jlayton@redhat.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@lst.de>,
	Josef Bacik <josef@toxicpanda.com>, Linux-MM <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.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 Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH] mm: Split page_has_private() in two to better handle PG_private_2
Date: Fri, 09 Apr 2021 09:14:24 +0100	[thread overview]
Message-ID: <184803.1617956064@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAHk-=wi_XrtTanTwoKs0jwnjhSvwpMYVDJ477VtjvvTXRjm5wQ@mail.gmail.com>

Linus Torvalds <torvalds@linux-foundation.org> wrote:

> >  #define PAGE_FLAGS_PRIVATE                             \
> >         (1UL << PG_private | 1UL << PG_private_2)
>
> I think this should be re-named to be PAGE_FLAGS_CLEANUP, because I
> don't think it makes any other sense to "combine" the two PG_private*
> bits any more. No?

Sure.  Do we even want it still, or should I just fold it into
page_needs_cleanup()?  It seems to be the only place it's used.

> > +static inline int page_private_count(struct page *page)
> > +{
> > +       return test_bit(PG_private, &page->flags) ? 1 : 0;
> > +}
>
> Why is this open-coding the bit test, rather than just doing
>
>         return PagePrivate(page) ? 1 : 0;
>
> instead? In fact, since test_bit() _should_ return a 'bool', I think even just
>
>         return PagePrivate(page);

Sorry, yes, it should be that.  I was looking at transforming the "1 <<
PG_private" and completely overlooked that this should be PagePrivate().

> should work and give the same result, but I could imagine that some
> architecture version of "test_bit()" might return some other non-zero
> value (although honestly, I think that should be fixed if so).

Yeah.  I seem to recall that test_bit() on some arches used to return the
datum just with the other bits masked off, but I may be misremembering.

In asm-generic/bitops/non-atomic.h:

static inline int test_bit(int nr, const volatile unsigned long *addr)
{
	return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}

should perhaps return bool?

I wonder, should:

	static __always_inline int PageTail(struct page *page)
	static __always_inline int PageCompound(struct page *page)
	static __always_inline int Page##uname(struct page *page)
	static __always_inline int TestSetPage##uname(struct page *page)
	static __always_inline int TestClearPage##uname(struct page *page)

also all return bool?

David


  parent reply	other threads:[~2021-04-09  8:14 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-08 14:03 [PATCH v6 00/30] Network fs helper library & fscache kiocb API David Howells
2021-04-08 14:04 ` [PATCH v6 01/30] iov_iter: Add ITER_XARRAY David Howells
2021-04-09  1:24   ` Al Viro
2021-04-09 18:10     ` [RFC PATCH 1/2] iov_iter: Remove iov_iter_for_each_range() David Howells
2021-04-09 18:11     ` [RFC PATCH 2/2] iov_iter: Drop the X argument from iterate_all_kinds() and use B instead David Howells
2021-04-09  9:09   ` [PATCH v6 01/30] iov_iter: Add ITER_XARRAY David Howells
2021-04-09 11:44     ` Matthew Wilcox
2021-04-22 13:35   ` Jeff Layton
2021-04-22 13:35     ` Jeff Layton
2021-04-22 13:51   ` David Howells
2021-04-22 14:51     ` Jeff Layton
2021-04-22 14:51       ` Jeff Layton
2021-04-08 14:04 ` [PATCH v6 02/30] mm: Add set/end/wait functions for PG_private_2 David Howells
2021-04-08 14:50   ` Matthew Wilcox
2021-04-08 15:25   ` David Howells
2021-04-08 15:57   ` David Howells
2021-04-08 21:15   ` [RFC][PATCH] mm: Split page_has_private() in two to better handle PG_private_2 David Howells
2021-04-08 23:50     ` Linus Torvalds
2021-04-08 23:50       ` Linus Torvalds
2021-04-09 10:59       ` [RFC PATCH 1/3] Make the generic bitops return bool David Howells
2021-04-09 10:59       ` [RFC PATCH 2/3] mm: Return bool from pagebit test functions David Howells
2021-04-09 11:16         ` Matthew Wilcox
2021-04-09 12:00         ` David Howells
2021-04-09 12:35         ` David Howells
2021-04-09 16:03         ` David Howells
2021-04-09 16:03           ` David Howells
2021-04-09 10:59       ` [RFC PATCH 3/3] mm: Split page_has_private() in two to better handle PG_private_2 David Howells
2021-04-09 11:24         ` Matthew Wilcox
2021-04-09  8:14     ` David Howells [this message]
2021-04-13 15:11   ` [PATCH v7] mm: Add set/end/wait functions for PG_private_2 David Howells
2021-04-13 15:22     ` Matthew Wilcox
2021-04-08 14:04 ` [PATCH v6 03/30] mm/filemap: Pass the file_ra_state in the ractl David Howells
2021-04-08 14:04 ` [PATCH v6 04/30] fs: Document file_ra_state David Howells
2021-04-08 14:04 ` [PATCH v6 05/30] mm: Implement readahead_control pageset expansion David Howells
2021-04-08 14:55   ` Matthew Wilcox
2021-04-08 14:05 ` [PATCH v6 06/30] netfs: Make a netfs helper module David Howells
2021-04-08 14:05 ` [PATCH v6 07/30] netfs: Documentation for helper library David Howells
2021-04-08 14:05 ` [PATCH v6 08/30] netfs, mm: Move PG_fscache helper funcs to linux/netfs.h David Howells
2021-04-08 14:05 ` [PATCH v6 09/30] netfs, mm: Add set/end/wait_on_page_fscache() aliases David Howells
2021-04-08 14:06 ` [PATCH v6 10/30] netfs: Provide readahead and readpage netfs helpers David Howells
2021-04-08 14:06 ` [PATCH v6 11/30] netfs: Add tracepoints David Howells
2021-04-08 14:06 ` [PATCH v6 12/30] netfs: Gather stats David Howells
2021-04-08 14:06 ` [PATCH v6 13/30] netfs: Add write_begin helper David Howells
2021-04-08 14:06 ` [PATCH v6 14/30] netfs: Define an interface to talk to a cache David Howells
2021-04-08 14:07 ` [PATCH v6 15/30] netfs: Add a tracepoint to log failures that would be otherwise unseen David Howells
2021-04-08 14:07 ` [PATCH v6 16/30] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-04-08 14:07 ` [PATCH v6 17/30] afs: Disable use of the fscache I/O routines David Howells
2021-04-08 14:07 ` [PATCH v6 18/30] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-04-08 14:08 ` [PATCH v6 19/30] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-04-08 14:08 ` [PATCH v6 20/30] afs: Move key to afs_read struct David Howells
2021-04-08 14:08 ` [PATCH v6 21/30] afs: Don't truncate iter during data fetch David Howells
2021-04-08 14:08 ` [PATCH v6 22/30] afs: Log remote unmarshalling errors David Howells
2021-04-08 14:08 ` [PATCH v6 23/30] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-04-08 14:09 ` [PATCH v6 24/30] afs: Use ITER_XARRAY for writing David Howells
2021-04-08 14:09 ` [PATCH v6 25/30] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-04-08 14:09 ` [PATCH v6 26/30] afs: Extract writeback extension into its own function David Howells
2021-04-08 14:09 ` [PATCH v6 27/30] afs: Prepare for use of THPs David Howells
2021-04-08 14:09 ` [PATCH v6 28/30] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-04-08 14:10 ` [PATCH v6 29/30] afs: Use new netfs lib read helper API David Howells
2021-04-08 14:10 ` [PATCH v6 30/30] afs: Use the netfs_write_begin() helper David Howells
2021-04-08 15:40 ` [PATCH v6 00/30] Network fs helper library & fscache kiocb API Jeff Layton
2021-04-08 15:40   ` Jeff Layton
2021-04-09 12:04 ` David Wysochanski
2021-04-09 12:04   ` David Wysochanski
2021-04-13 14:56   ` David Wysochanski
2021-04-13 14:56     ` David Wysochanski
2021-04-13 16:21 ` Marc Dionne
2021-04-13 16:21   ` Marc Dionne

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