From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752472AbcKQWUO (ORCPT ); Thu, 17 Nov 2016 17:20:14 -0500 Received: from mail-pf0-f178.google.com ([209.85.192.178]:32804 "EHLO mail-pf0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752277AbcKQWUK (ORCPT ); Thu, 17 Nov 2016 17:20:10 -0500 Date: Thu, 17 Nov 2016 14:20:08 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Douglas Anderson cc: Alasdair Kergon , Mike Snitzer , Dmitry Torokhov , Sonny Rao , linux@roeck-us.net, dm-devel@redhat.com, shli@kernel.org, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] RFC: dm: avoid the mutex lock in dm_bufio_shrink_count() In-Reply-To: <1479417398-2593-1-git-send-email-dianders@chromium.org> Message-ID: References: <1479417398-2593-1-git-send-email-dianders@chromium.org> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Nov 2016, Douglas Anderson wrote: > diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c > index b3ba142e59a4..885ba5482d9f 100644 > --- a/drivers/md/dm-bufio.c > +++ b/drivers/md/dm-bufio.c > @@ -89,6 +89,7 @@ struct dm_bufio_client { > > struct list_head lru[LIST_SIZE]; > unsigned long n_buffers[LIST_SIZE]; > + unsigned long n_all_buffers; > > struct block_device *bdev; > unsigned block_size; > @@ -485,6 +486,7 @@ static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty) > struct dm_bufio_client *c = b->c; > > c->n_buffers[dirty]++; > + c->n_all_buffers++; > b->block = block; > b->list_mode = dirty; > list_add(&b->lru_list, &c->lru[dirty]); > @@ -502,6 +504,7 @@ static void __unlink_buffer(struct dm_buffer *b) > BUG_ON(!c->n_buffers[b->list_mode]); > > c->n_buffers[b->list_mode]--; > + c->n_all_buffers--; > __remove(b->c, b); > list_del(&b->lru_list); > } > @@ -515,6 +518,7 @@ static void __relink_lru(struct dm_buffer *b, int dirty) > > BUG_ON(!c->n_buffers[b->list_mode]); > > + /* NOTE: don't update n_all_buffers: -1 + 1 = 0 */ > c->n_buffers[b->list_mode]--; > c->n_buffers[dirty]++; > b->list_mode = dirty; > @@ -1588,17 +1592,10 @@ static unsigned long > dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc) > { > struct dm_bufio_client *c; > - unsigned long count; > > c = container_of(shrink, struct dm_bufio_client, shrinker); > - if (sc->gfp_mask & __GFP_FS) > - dm_bufio_lock(c); > - else if (!dm_bufio_trylock(c)) > - return 0; > > - count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY]; > - dm_bufio_unlock(c); > - return count; > + return c->n_all_buffers; > } > > /* Would be better to just avoid taking the mutex at all and returning c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY] with a comment that the estimate might be wrong, but the actual count may vary between ->count_objects() and ->scan_objects() anyway, so we don't actually care?