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Mon, 31 Mar 2025 03:52:56 -0700 (PDT) Date: Mon, 31 Mar 2025 12:52:55 +0200 From: Michal Hocko To: 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, vbabka@suse.cz, bigeasy@linutronix.de, rostedt@goodmis.org, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH mm] mm/page_alloc: Avoid second trylock of zone->lock Message-ID: References: <20250331002809.94758-1-alexei.starovoitov@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250331002809.94758-1-alexei.starovoitov@gmail.com> 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 and will execute redundant irq restore/save pair. > Therefore, check alloc/fpi_flags first and use spin_trylock or > spin_lock. > > 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. Acked-by: Michal Hocko 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 -- Michal Hocko SUSE Labs