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bh=wMtih/JfshDEE/Jc8JTNUYdJycairy8oF4UI8O3/Rn4=; b=zOyf1ZQgJBH2Wd9QN5YBb8aHU6emyEiYo+Swy61v+TbC6PHk17i4WPpadWh756aTNbTwsH 8lmDRtXjBn0FMaDw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 64617136A5; Tue, 29 Oct 2024 16:48:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 0FgyGOkRIWeiKwAAD6G6ig (envelope-from ); Tue, 29 Oct 2024 16:48:41 +0000 Message-ID: <3febb57e-e805-4cb9-8929-e47b957192a6@suse.cz> Date: Tue, 29 Oct 2024 17:48:41 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 tip/perf/core 2/4] mm: Introduce mmap_lock_speculation_{begin|end} Content-Language: en-US To: Andrii Nakryiko , linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, peterz@infradead.org Cc: oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, shakeel.butt@linux.dev, hannes@cmpxchg.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, arnd@arndb.de, richard.weiyang@gmail.com, zhangpeng.00@bytedance.com, linmiaohe@huawei.com, viro@zeniv.linux.org.uk, hca@linux.ibm.com References: <20241028010818.2487581-1-andrii@kernel.org> <20241028010818.2487581-3-andrii@kernel.org> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9C89E1FDF3 X-Spam-Level: X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; ARC_NA(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[29]; MIME_TRACE(0.00)[0:+]; FREEMAIL_CC(0.00)[redhat.com,goodmis.org,kernel.org,vger.kernel.org,infradead.org,google.com,gmail.com,linux.dev,cmpxchg.org,oracle.com,arndb.de,bytedance.com,huawei.com,zeniv.linux.org.uk,linux.ibm.com]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RL9sdddhhbu1oo5wyhn6sr3k5b)]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:email,suse.cz:dkim,suse.cz:mid,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -3.01 X-Spam-Flag: NO On 10/28/24 02:08, Andrii Nakryiko wrote: > From: Suren Baghdasaryan > > Add helper functions to speculatively perform operations without > read-locking mmap_lock, expecting that mmap_lock will not be > write-locked and mm is not modified from under us. > > Suggested-by: Peter Zijlstra > Signed-off-by: Suren Baghdasaryan > Signed-off-by: Andrii Nakryiko Acked-by: Vlastimil Babka > --- > include/linux/mmap_lock.h | 29 +++++++++++++++++++++++++++-- > 1 file changed, 27 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h > index 6b3272686860..58dde2e35f7e 100644 > --- a/include/linux/mmap_lock.h > +++ b/include/linux/mmap_lock.h > @@ -71,6 +71,7 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm) > } > > #ifdef CONFIG_PER_VMA_LOCK > + > static inline void mm_lock_seqcount_init(struct mm_struct *mm) > { > seqcount_init(&mm->mm_lock_seq); > @@ -86,11 +87,35 @@ static inline void mm_lock_seqcount_end(struct mm_struct *mm) > do_raw_write_seqcount_end(&mm->mm_lock_seq); > } > > -#else > +static inline bool mmap_lock_speculation_begin(struct mm_struct *mm, unsigned int *seq) > +{ > + *seq = raw_read_seqcount(&mm->mm_lock_seq); > + /* Allow speculation if mmap_lock is not write-locked */ > + return (*seq & 1) == 0; > +} > + > +static inline bool mmap_lock_speculation_end(struct mm_struct *mm, unsigned int seq) > +{ > + return !do_read_seqcount_retry(&mm->mm_lock_seq, seq); > +} > + > +#else /* CONFIG_PER_VMA_LOCK */ > + > static inline void mm_lock_seqcount_init(struct mm_struct *mm) {} > static inline void mm_lock_seqcount_begin(struct mm_struct *mm) {} > static inline void mm_lock_seqcount_end(struct mm_struct *mm) {} > -#endif > + > +static inline bool mmap_lock_speculation_begin(struct mm_struct *mm, unsigned int *seq) > +{ > + return false; > +} > + > +static inline bool mmap_lock_speculation_end(struct mm_struct *mm, unsigned int seq) > +{ > + return false; > +} > + > +#endif /* CONFIG_PER_VMA_LOCK */ > > static inline void mmap_init_lock(struct mm_struct *mm) > {