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[90.233.217.52]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-54d3d51ffa1sm1426337e87.228.2025.04.15.08.25.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Apr 2025 08:25:41 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 15 Apr 2025 17:25:39 +0200 To: Baoquan He Cc: linux-mm@kvack.org, akpm@linux-foundation.org, urezki@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/5] mm/vmalloc.c: find the vmap of vmap_nodes in reverse order Message-ID: References: <20250415023952.27850-1-bhe@redhat.com> <20250415023952.27850-3-bhe@redhat.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: <20250415023952.27850-3-bhe@redhat.com> On Tue, Apr 15, 2025 at 10:39:49AM +0800, Baoquan He wrote: > When finding VA in vn->busy, if VA spans several zones and the passed > addr is not the same as va->va_start, we should scan the vn in reverse > odrdr because the starting address of VA must be smaller than the passed > addr if it really resides in the VA. > > E.g on a system nr_vmap_nodes=100, > > <----va----> > -|-----|-----|-----|-----|-----|-----|-----|-----|-----|- > ... n-1 n n+1 n+2 ... 100 0 1 > > VA resides in node 'n' whereas it spans 'n', 'n+1' and 'n+2'. If passed > addr is within 'n+2', we should try nodes backwards on 'n+1' and 'n', > then succeed very soon. > > Meanwhile we still need loop around because VA could spans node from 'n' > to node 100, node 0, node 1. > > Anyway, changing to find in reverse order can improve efficiency on > many CPUs system. > > Signed-off-by: Baoquan He > --- > mm/vmalloc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index aca1905d3397..488d69b56765 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2436,7 +2436,7 @@ struct vmap_area *find_vmap_area(unsigned long addr) > > if (va) > return va; > - } while ((i = (i + 1) % nr_vmap_nodes) != j); > + } while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j); > > return NULL; > } > @@ -2462,7 +2462,7 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr) > > if (va) > return va; > - } while ((i = (i + 1) % nr_vmap_nodes) != j); > + } while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j); > > return NULL; > } > -- > 2.41.0 > It depends. Consider a below situation: addr | VA V <------------> <---|---|---|---|---|---|---|---> 0 1 2 3 0 1 2 3 basically it matters how big VA and how many nodes it spans. But i agree that an assumption to reverse back is more convinced in most cases. Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki