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Tue, 15 Apr 2025 14:05:08 +0000 (UTC) Date: Tue, 15 Apr 2025 22:05:04 +0800 From: Baoquan He To: Shivank Garg Cc: linux-mm@kvack.org, akpm@linux-foundation.org, urezki@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/5] mm/vmalloc.c: optimize code in decay_va_pool_node() a little bit Message-ID: References: <20250415023952.27850-1-bhe@redhat.com> <20250415023952.27850-4-bhe@redhat.com> <8d83441f-9f67-4094-81b6-70cd5db88acb@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d83441f-9f67-4094-81b6-70cd5db88acb@amd.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspam-User: X-Rspamd-Queue-Id: 0B32F40014 X-Rspamd-Server: rspam04 X-Stat-Signature: 8fs4ent688xhbccmnb6y17fqa7bx34z7 X-HE-Tag: 1744725917-535352 X-HE-Meta: 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 TPw+iPcu Rc3AcLI4Fbmn3HoKK05LOdFNVyC8+7zsdhrYbRiPa2gP5gr/iykeF4wQnkhOIqRBlV1Ap/fWoNKRcLGzaeruKYEHZEvxJf/tjtwM85ldrpwcqghgs1Q9pqID/JeV/dSY2WZQIlacVfQ5LI85wUpMZA0k73WVWjIsmCF+4mqrOwtzmwWnlJsUzJhTTDxnWk1wgBc+qhoSDXWiz4acCKoYnyATDCxljG+Dr5asznab+dI2TYvX3DDzIGUKyoBdVq6ZK7cqo/huTTqeNTvmBNODgXA4eB7YAFhoBjoNMu7IX4QeplOv5wmmidp3u2opV3/gL++3pHyODuzAH3xLltOCw9PDK5xeyGydc3U+KBhL1QC+Nn1RvD6/8iKrV7C7WcL08mkbj9ZjDmZ5iZJoOIk5ujOcZdbAxnrPkJoWP8v/rhg6758ZAHRIwguNu+g== 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 04/15/25 at 03:59pm, Shivank Garg wrote: > On 4/15/2025 8:09 AM, Baoquan He wrote: > > When purge lazily freed vmap areas, VA stored in vn->pool[] will also be > > taken away into free vmap tree partially or completely accordingly, that > > is done in decay_va_pool_node(). When doing that, for each pool of node, > > the whole list is detached from the pool for handling. At this time, > > that pool is empty. It's not necessary to update the pool size each time > > when one VA is removed and addded into free vmap tree. > > > > Here change code to update the pool size when attaching the pool back. > > > > Signed-off-by: Baoquan He > > --- > > mm/vmalloc.c | 23 +++++++++++------------ > > 1 file changed, 11 insertions(+), 12 deletions(-) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 488d69b56765..bf735c890878 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -2150,7 +2150,7 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay) > > LIST_HEAD(decay_list); > > struct rb_root decay_root = RB_ROOT; > > struct vmap_area *va, *nva; > > - unsigned long n_decay; > > + unsigned long n_decay, len; > > int i; > > > > for (i = 0; i < MAX_VA_SIZE_PAGES; i++) { > > @@ -2164,22 +2164,20 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay) > > list_replace_init(&vn->pool[i].head, &tmp_list); > > spin_unlock(&vn->pool_lock); > > > > - if (full_decay) > > - WRITE_ONCE(vn->pool[i].len, 0); > > + len = n_decay = vn->pool[i].len; > > + WRITE_ONCE(vn->pool[i].len, 0); > > > > /* Decay a pool by ~25% out of left objects. */ > > - n_decay = vn->pool[i].len >> 2; > > + if (!full_decay) > > + n_decay >>= 2; > > + len -= n_decay; > > > > list_for_each_entry_safe(va, nva, &tmp_list, list) { > > + if (!n_decay) > > + break; > > list_del_init(&va->list); > > merge_or_add_vmap_area(va, &decay_root, &decay_list); > > - > > - if (!full_decay) { > > - WRITE_ONCE(vn->pool[i].len, vn->pool[i].len - 1); > > - > > - if (!--n_decay) > > - break; > > - } > > + n_decay--; > > } > > > > /* > > @@ -2188,9 +2186,10 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay) > > * can populate the pool therefore a simple list replace > > * operation takes place here. > > */ > > - if (!full_decay && !list_empty(&tmp_list)) { > > + if (!list_empty(&tmp_list)) { > > spin_lock(&vn->pool_lock); > > list_replace_init(&tmp_list, &vn->pool[i].head); > > + vn->pool[i].len = len; > > Current logic uses WRITE_ONCE() to update vn->pool[i].len. > Could this lead to consistency issues? Seems no necessary to use WRITE_ONCE(). I can change back to use WRITE_ONCE() just in case. Currently, it's only updated in node_alloc(), decay_va_pool_node(), purge_vmap_node(). And the latter two are inside vmap_purge_lock area. > > > spin_unlock(&vn->pool_lock); > > } > > } >