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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH v5 9/9] bio: Fix bio_flagged() so that it can be combined From: David Howells To: Al Viro Cc: Jens Axboe , linux-block@vger.kernel.org, dhowells@redhat.com, Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 11 Jan 2023 14:28:42 +0000 Message-ID: <167344732239.2425628.14636562879255014501.stgit@warthog.procyon.org.uk> In-Reply-To: <167344725490.2425628.13771289553670112965.stgit@warthog.procyon.org.uk> References: <167344725490.2425628.13771289553670112965.stgit@warthog.procyon.org.uk> User-Agent: StGit/1.5 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Fix bio_flagged() so that multiple instances of it can be combined by the compiler into a single test (arguably, this is a compiler optimisation issue[1]). The problem is that it compares the result of the bitwise-AND to zero. This results in an out-of-line bio_release_page() that looks something like: <+0>: mov 0x14(%rdi),%eax <+3>: test $0x1,%al <+5>: jne 0xffffffff816dac53 <+7>: test $0x2,%al <+9>: je 0xffffffff816dac5c <+11>: movzbl %sil,%esi <+15>: jmp 0xffffffff816daba1 <__bio_release_pages> <+20>: jmp 0xffffffff81d0b800 <__x86_return_thunk> Removing the test (it's superfluous as the return type is bool - the compiler will reduce the return to 0 or 1 as needed) results in: <+0>: testb $0x3,0x14(%rdi) <+4>: je 0xffffffff816e4af4 <+6>: movzbl %sil,%esi <+10>: jmp 0xffffffff816dab7c <__bio_release_pages> <+15>: jmp 0xffffffff81d0b7c0 <__x86_return_thunk> instead. The MOVZBL instruction also looks unnecessary[2] - I think it's just 're-booling' the mark_dirty. Fixes: b7c44ed9d2fc ("block: manipulate bio->bi_flags through helpers") Signed-off-by: David Howells cc: Jens Axboe cc: linux-block@vger.kernel.org Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108370 [1] Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108371 [2] --- include/linux/bio.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/bio.h b/include/linux/bio.h index 1c6f051f6ff2..2e6109b0fca8 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -227,7 +227,7 @@ static inline void bio_cnt_set(struct bio *bio, unsigne= d int count) =20 static inline bool bio_flagged(struct bio *bio, unsigned int bit) { - return (bio->bi_flags & (1U << bit)) !=3D 0; + return bio->bi_flags & (1U << bit); } =20 static inline void bio_set_flag(struct bio *bio, unsigned int bit)