From: Matthew Wilcox <willy@infradead.org>
To: David Laight <David.Laight@aculab.com>
Cc: Greg Ungerer <gregungerer@westnet.com.au>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH 09/17] m68k: Implement xor_unlock_is_negative_byte
Date: Tue, 19 Sep 2023 16:47:21 +0100 [thread overview]
Message-ID: <ZQnCiZuMbFnwbEUt@casper.infradead.org> (raw)
In-Reply-To: <c61a58a1f5a34f2b96c6043840635197@AcuMS.aculab.com>
On Tue, Sep 19, 2023 at 03:22:25PM +0000, David Laight wrote:
> > Anyway, that's not the brief. We're looking to (eg) clear bit 0
> > and test whether bit 7 was set. So it's the sign bit of the byte,
> > not the sign bit of the int.
>
> Use the address of the byte as an int and xor with 1u<<24.
> The xor will do a rmw on the three bytes following, but I
> doubt that matters.
Bet you a shiny penny that Coldfire takes an unaligned access trap ...
and besides, this is done on _every_ call to unlock_page(). That might
cross not only a cacheline boundary but also a page boundary. I cannot
believe that would be a high-performing solution. It might be just fine
on m68000 but I bet even by the 030 it's lower performing.
next prev parent reply other threads:[~2023-09-19 15:47 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-15 18:36 [PATCH 00/17] Add folio_end_read Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 01/17] iomap: Hold state_lock over call to ifs_set_range_uptodate() Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 02/17] iomap: Protect read_bytes_pending with the state_lock Matthew Wilcox (Oracle)
2023-09-16 0:11 ` Linus Torvalds
2023-09-16 0:15 ` Linus Torvalds
2023-09-16 15:50 ` Matthew Wilcox
2023-09-15 18:36 ` [PATCH 03/17] mm: Add folio_end_read() Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 04/17] ext4: Use folio_end_read() Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 05/17] buffer: " Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 06/17] iomap: " Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 07/17] bitops: Add xor_unlock_is_negative_byte() Matthew Wilcox (Oracle)
2023-09-15 18:36 ` [PATCH 08/17] alpha: Implement xor_unlock_is_negative_byte Matthew Wilcox (Oracle)
2023-09-16 0:27 ` Linus Torvalds
2023-09-16 0:38 ` Matthew Wilcox
2023-09-16 2:01 ` Linus Torvalds
2023-09-16 2:14 ` Linus Torvalds
2023-09-16 15:59 ` Matthew Wilcox
2023-09-15 18:36 ` [PATCH 09/17] m68k: " Matthew Wilcox (Oracle)
2023-09-16 13:11 ` Greg Ungerer
2023-09-16 14:34 ` Matthew Wilcox
2023-09-18 14:37 ` Greg Ungerer
2023-09-20 7:45 ` Greg Ungerer
2023-09-20 16:58 ` Linus Torvalds
2023-09-19 13:23 ` David Laight
2023-09-19 14:26 ` Matthew Wilcox
2023-09-19 14:35 ` David Laight
2023-09-19 15:14 ` Matthew Wilcox
2023-09-19 15:22 ` David Laight
2023-09-19 15:47 ` Matthew Wilcox [this message]
2023-09-19 15:57 ` David Laight
2023-09-20 7:15 ` Greg Ungerer
2023-09-20 7:22 ` Greg Ungerer
2023-10-02 20:07 ` Matthew Wilcox
2023-10-03 14:14 ` Greg Ungerer
2023-10-03 20:07 ` Matthew Wilcox
2023-10-04 12:06 ` Greg Ungerer
2023-09-15 18:37 ` [PATCH 10/17] mips: " Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 11/17] powerpc: Implement arch_xor_unlock_is_negative_byte on 32-bit Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 12/17] riscv: Implement xor_unlock_is_negative_byte Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 13/17] s390: Implement arch_xor_unlock_is_negative_byte Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 14/17] mm: Delete checks for xor_unlock_is_negative_byte() Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 15/17] mm: Add folio_xor_flags_has_waiters() Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 16/17] mm: Make __end_folio_writeback() return void Matthew Wilcox (Oracle)
2023-09-15 18:37 ` [PATCH 17/17] mm: Use folio_xor_flags_has_waiters() in folio_end_writeback() Matthew Wilcox (Oracle)
2023-09-16 0:31 ` [PATCH 00/17] Add folio_end_read Linus Torvalds
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