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Mon, 31 Mar 2025 12:17:50 +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 tlWfFO6H6mfJCQAAD6G6ig (envelope-from ); Mon, 31 Mar 2025 12:17:50 +0000 Message-ID: Date: Mon, 31 Mar 2025 14:17:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm] mm/page_alloc: Avoid second trylock of zone->lock Content-Language: en-US To: Michal Hocko , Alexei Starovoitov Cc: Linus Torvalds , bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, akpm@linux-foundation.org, peterz@infradead.org, bigeasy@linutronix.de, rostedt@goodmis.org, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250331002809.94758-1-alexei.starovoitov@gmail.com> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 7DE66120013 X-Stat-Signature: uogqns4x6j7wos1qrpgwud36wqmchf8i X-HE-Tag: 1743423472-974189 X-HE-Meta: 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 9ah31F7V 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/31/25 12:52, Michal Hocko wrote: > On Sun 30-03-25 17:28:09, Alexei Starovoitov wrote: >> From: Alexei Starovoitov >> >> spin_trylock followed by spin_lock will cause extra write cache >> access. If the lock is contended it may cause unnecessary cache >> line bouncing Right. > and will execute redundant irq restore/save pair. Maybe that part matters less if we're likely to have to spin anyway - it doesn't affect other cpus at least unlike the bouncing. >> Therefore, check alloc/fpi_flags first and use spin_trylock or >> spin_lock. Yeah this should be still ok for the zone lock as the fast paths are using pcplists, so we still shouldn't be making page allocator slower due to the try_alloc addition. >> Suggested-by: Linus Torvalds >> Fixes: 97769a53f117 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation") >> Signed-off-by: Alexei Starovoitov > > Makes sense. Fixes tag is probably over reaching but whatever. It's fixing 6.15-rc1 code so no possible stable implications anyway. > Acked-by: Michal Hocko Acked-by: Vlastimil Babka > Thanks! > >> --- >> mm/page_alloc.c | 15 +++++++++------ >> 1 file changed, 9 insertions(+), 6 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index e3ea5bf5c459..ffbb5678bc2f 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -1268,11 +1268,12 @@ static void free_one_page(struct zone *zone, struct page *page, >> struct llist_head *llhead; >> unsigned long flags; >> >> - if (!spin_trylock_irqsave(&zone->lock, flags)) { >> - if (unlikely(fpi_flags & FPI_TRYLOCK)) { >> + if (unlikely(fpi_flags & FPI_TRYLOCK)) { >> + if (!spin_trylock_irqsave(&zone->lock, flags)) { >> add_page_to_zone_llist(zone, page, order); >> return; >> } >> + } else { >> spin_lock_irqsave(&zone->lock, flags); >> } >> >> @@ -2341,9 +2342,10 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, >> unsigned long flags; >> int i; >> >> - if (!spin_trylock_irqsave(&zone->lock, flags)) { >> - if (unlikely(alloc_flags & ALLOC_TRYLOCK)) >> + if (unlikely(alloc_flags & ALLOC_TRYLOCK)) { >> + if (!spin_trylock_irqsave(&zone->lock, flags)) >> return 0; >> + } else { >> spin_lock_irqsave(&zone->lock, flags); >> } >> for (i = 0; i < count; ++i) { >> @@ -2964,9 +2966,10 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, >> >> do { >> page = NULL; >> - if (!spin_trylock_irqsave(&zone->lock, flags)) { >> - if (unlikely(alloc_flags & ALLOC_TRYLOCK)) >> + if (unlikely(alloc_flags & ALLOC_TRYLOCK)) { >> + if (!spin_trylock_irqsave(&zone->lock, flags)) >> return NULL; >> + } else { >> spin_lock_irqsave(&zone->lock, flags); >> } >> if (alloc_flags & ALLOC_HIGHATOMIC) >> -- >> 2.47.1 >