From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f41.google.com (mail-pa0-f41.google.com [209.85.220.41]) by kanga.kvack.org (Postfix) with ESMTP id 10B456B006E for ; Mon, 29 Jun 2015 02:45:37 -0400 (EDT) Received: by pactm7 with SMTP id tm7so100137886pac.2 for ; Sun, 28 Jun 2015 23:45:36 -0700 (PDT) Received: from mail-pd0-x234.google.com (mail-pd0-x234.google.com. [2607:f8b0:400e:c02::234]) by mx.google.com with ESMTPS id a8si22443185pdl.110.2015.06.28.23.45.36 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Jun 2015 23:45:36 -0700 (PDT) Received: by pdjn11 with SMTP id n11so111617376pdj.0 for ; Sun, 28 Jun 2015 23:45:35 -0700 (PDT) Date: Mon, 29 Jun 2015 15:45:46 +0900 From: Minchan Kim Subject: Re: [RFC][PATCHv3 4/7] zsmalloc: introduce zs_can_compact() function Message-ID: <20150629064546.GB13179@bbox> References: <1434628004-11144-1-git-send-email-sergey.senozhatsky@gmail.com> <1434628004-11144-5-git-send-email-sergey.senozhatsky@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434628004-11144-5-git-send-email-sergey.senozhatsky@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky On Thu, Jun 18, 2015 at 08:46:41PM +0900, Sergey Senozhatsky wrote: > This function checks if class compaction will free any pages. > Rephrasing -- do we have enough unused objects to form at least > one ZS_EMPTY page and free it. It aborts compaction if class > compaction will not result in any (further) savings. > > EXAMPLE (this debug output is not part of this patch set): > > -- class size > -- number of allocated objects > -- number of used objects > -- max objects per zspage > -- pages per zspage > -- estimated number of pages that will be freed > > [..] > class-512 objs:544 inuse:540 maxobj-per-zspage:8 pages-per-zspage:1 zspages-to-free:0 > ... class-512 compaction is useless. break > class-496 objs:660 inuse:570 maxobj-per-zspage:33 pages-per-zspage:4 zspages-to-free:2 > class-496 objs:627 inuse:570 maxobj-per-zspage:33 pages-per-zspage:4 zspages-to-free:1 > class-496 objs:594 inuse:570 maxobj-per-zspage:33 pages-per-zspage:4 zspages-to-free:0 > ... class-496 compaction is useless. break > class-448 objs:657 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:4 > class-448 objs:648 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:3 > class-448 objs:639 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:2 > class-448 objs:630 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:1 > class-448 objs:621 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:0 > ... class-448 compaction is useless. break > class-432 objs:728 inuse:685 maxobj-per-zspage:28 pages-per-zspage:3 zspages-to-free:1 > class-432 objs:700 inuse:685 maxobj-per-zspage:28 pages-per-zspage:3 zspages-to-free:0 > ... class-432 compaction is useless. break > class-416 objs:819 inuse:705 maxobj-per-zspage:39 pages-per-zspage:4 zspages-to-free:2 > class-416 objs:780 inuse:705 maxobj-per-zspage:39 pages-per-zspage:4 zspages-to-free:1 > class-416 objs:741 inuse:705 maxobj-per-zspage:39 pages-per-zspage:4 zspages-to-free:0 > ... class-416 compaction is useless. break > class-400 objs:690 inuse:674 maxobj-per-zspage:10 pages-per-zspage:1 zspages-to-free:1 > class-400 objs:680 inuse:674 maxobj-per-zspage:10 pages-per-zspage:1 zspages-to-free:0 > ... class-400 compaction is useless. break > class-384 objs:736 inuse:709 maxobj-per-zspage:32 pages-per-zspage:3 zspages-to-free:0 > ... class-384 compaction is useless. break > [..] > > Every "compaction is useless" indicates that we saved CPU cycles. > > class-512 has > 544 object allocated > 540 objects used > 8 objects per-page > > Even if we have a ALMOST_EMPTY zspage, we still don't have enough room to > migrate all of its objects and free this zspage; so compaction will not > make a lot of sense, it's better to just leave it as is. > > Signed-off-by: Sergey Senozhatsky > --- > mm/zsmalloc.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 4b6f12e..18e10a4 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1684,6 +1684,28 @@ static struct page *isolate_source_page(struct size_class *class) > return page; > } > > +/* > + * Make sure that we actually can compact this class, > + * IOW if migration will release at least one szpage. zspage, > + * > + * Should be called under class->lock Please comment about return. > + */ > +static unsigned long zs_can_compact(struct size_class *class) > +{ > + /* > + * Calculate how many unused allocated objects we > + * have and see if we can free any zspages. Otherwise, > + * compaction can just move objects back and forth w/o > + * any memory gain. > + */ > + unsigned long obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) - > + zs_stat_get(class, OBJ_USED); > + I want to check one more thing. We could have lots of ZS_ALMOST_FULL but no ZS_ALMOST_EMPTY. In this implementation, compaction cannot have a source so it would better to bail out. IOW, if (!zs_stat_get(class, CLASS_ALMOST_EMPTY)) return 0; > + obj_wasted /= get_maxobj_per_zspage(class->size, > + class->pages_per_zspage); > + return obj_wasted; > +} > + > static unsigned long __zs_compact(struct zs_pool *pool, > struct size_class *class) > { > @@ -1697,6 +1719,9 @@ static unsigned long __zs_compact(struct zs_pool *pool, > > BUG_ON(!is_first_page(src_page)); > > + if (!zs_can_compact(class)) > + break; > + > cc.index = 0; > cc.s_page = src_page; > > -- > 2.4.4 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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