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[95.193.70.101]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-529be969ab2sm160302e87.150.2024.05.28.11.36.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 May 2024 11:36:02 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 28 May 2024 20:36:00 +0200 To: Uros Bizjak Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Dennis Zhou , Tejun Heo , Christoph Lameter Subject: Re: [PATCH v2 2/2] mm/vmalloc: Use __this_cpu_try_cmpxchg() in preload_this_cpu_lock() Message-ID: References: <20240528144345.5980-1-ubizjak@gmail.com> <20240528144345.5980-2-ubizjak@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: <20240528144345.5980-2-ubizjak@gmail.com> On Tue, May 28, 2024 at 04:43:14PM +0200, Uros Bizjak wrote: > Use __this_cpu_try_cmpxchg() instead of > __this_cpu_cmpxchg (*ptr, old, new) == old in > preload_this_cpu_lock(). x86 CMPXCHG instruction returns > success in ZF flag, so this change saves a compare after cmpxchg. > > The generated code improves from: > > 4bb6: 48 85 f6 test %rsi,%rsi > 4bb9: 0f 84 10 fa ff ff je 45cf <...> > 4bbf: 4c 89 e8 mov %r13,%rax > 4bc2: 65 48 0f b1 35 00 00 cmpxchg %rsi,%gs:0x0(%rip) > 4bc9: 00 00 > 4bcb: 48 85 c0 test %rax,%rax > 4bce: 0f 84 fb f9 ff ff je 45cf <...> > > to: > > 4bb6: 48 85 f6 test %rsi,%rsi > 4bb9: 0f 84 10 fa ff ff je 45cf <...> > 4bbf: 4c 89 e8 mov %r13,%rax > 4bc2: 65 48 0f b1 35 00 00 cmpxchg %rsi,%gs:0x0(%rip) > 4bc9: 00 00 > 4bcb: 0f 84 fe f9 ff ff je 45cf <...> > > No functional change intended. > > Signed-off-by: Uros Bizjak > Cc: Andrew Morton > Cc: Uladzislau Rezki > Cc: Christoph Hellwig > Cc: Lorenzo Stoakes > Cc: Dennis Zhou > Cc: Tejun Heo > Cc: Christoph Lameter > --- > v2: Show generated code improvement in the commit message. > --- > mm/vmalloc.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 5d3aa2dc88a8..4f34d935d648 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1816,7 +1816,7 @@ static void free_vmap_area(struct vmap_area *va) > static inline void > preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node) > { > - struct vmap_area *va = NULL; > + struct vmap_area *va = NULL, *tmp; > > /* > * Preload this CPU with one extra vmap_area object. It is used > @@ -1832,7 +1832,8 @@ preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node) > > spin_lock(lock); > > - if (va && __this_cpu_cmpxchg(ne_fit_preload_node, NULL, va)) > + tmp = NULL; > + if (va && !__this_cpu_try_cmpxchg(ne_fit_preload_node, &tmp, va)) > kmem_cache_free(vmap_area_cachep, va); > } > > -- > 2.42.0 > Reviewed-by: Uladzislau Rezki (Sony) Thanks! -- Uladzislau Rezki