From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756578AbbFPOTZ (ORCPT ); Tue, 16 Jun 2015 10:19:25 -0400 Received: from mail-pa0-f43.google.com ([209.85.220.43]:35556 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756019AbbFPOTW (ORCPT ); Tue, 16 Jun 2015 10:19:22 -0400 Date: Tue, 16 Jun 2015 23:19:14 +0900 From: Minchan Kim To: Sergey Senozhatsky Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC][PATCHv2 5/8] zsmalloc: introduce zs_can_compact() function Message-ID: <20150616141914.GC31387@blaptop> References: <1433505838-23058-1-git-send-email-sergey.senozhatsky@gmail.com> <1433505838-23058-6-git-send-email-sergey.senozhatsky@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1433505838-23058-6-git-send-email-sergey.senozhatsky@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 05, 2015 at 09:03:55PM +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, > -- estimated number of pages that will be freed > > [..] > class-3072 objs:24652 inuse:24628 maxobjs-per-page:4 pages-tofree:6 Please use clear term. We have been used zspage as cluster of pages. maxobjs-per-zspage:4 And say what is pages-per-zspage for each class. then, write how you calculate it for easy reviewing. * class-3072 * pages-per-zspage: 3 * maxobjs-per-zspage = 4 In your example, allocated obj = 24652 and inuse obj = 24628 so 24652 - 24628 = 24 = 4(ie, maxobjs-per-zspage) * 6 so we can save 6 zspage. A zspage includes 3 pages so we can save 3 * 6 = 18 pages via compaction. > class-3072 objs:24648 inuse:24628 maxobjs-per-page:4 pages-tofree:5 > class-3072 objs:24644 inuse:24628 maxobjs-per-page:4 pages-tofree:4 > class-3072 objs:24640 inuse:24628 maxobjs-per-page:4 pages-tofree:3 > class-3072 objs:24636 inuse:24628 maxobjs-per-page:4 pages-tofree:2 > class-3072 objs:24632 inuse:24628 maxobjs-per-page:4 pages-tofree:1 > class-2720 objs:17970 inuse:17966 maxobjs-per-page:3 pages-tofree:1 > class-2720 objs:17967 inuse:17966 maxobjs-per-page:3 pages-tofree:0 > class-2720: Compaction is useless > class-2448 objs:7680 inuse:7674 maxobjs-per-page:5 pages-tofree:1 > class-2336 objs:13510 inuse:13500 maxobjs-per-page:7 pages-tofree:1 > class-2336 objs:13503 inuse:13500 maxobjs-per-page:7 pages-tofree:0 > class-2336: Compaction is useless > class-1808 objs:1161 inuse:1154 maxobjs-per-page:9 pages-tofree:0 > class-1808: Compaction is useless > class-1744 objs:2135 inuse:2131 maxobjs-per-page:7 pages-tofree:0 > class-1744: Compaction is useless > class-1536 objs:1328 inuse:1323 maxobjs-per-page:8 pages-tofree:0 > class-1536: Compaction is useless > class-1488 objs:8855 inuse:8847 maxobjs-per-page:11 pages-tofree:0 > class-1488: Compaction is useless > class-1360 objs:14880 inuse:14878 maxobjs-per-page:3 pages-tofree:0 > class-1360: Compaction is useless > class-1248 objs:3588 inuse:3577 maxobjs-per-page:13 pages-tofree:0 > class-1248: Compaction is useless > class-1216 objs:3380 inuse:3372 maxobjs-per-page:10 pages-tofree:0 > class-1216: Compaction is useless > class-1168 objs:3416 inuse:3401 maxobjs-per-page:7 pages-tofree:2 > class-1168 objs:3409 inuse:3401 maxobjs-per-page:7 pages-tofree:1 > class-1104 objs:605 inuse:599 maxobjs-per-page:11 pages-tofree:0 > class-1104: Compaction is useless > [..] > > Every "Compaction is useless" indicates that we saved some CPU cycles. > > class-1104 has > 605 object allocated > 599 objects used > 11 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 here, 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 0453347..5d8f1d4 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1682,6 +1682,28 @@ 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 empty at least one page. free at least one zspage > + * > + * Should be called under class->lock > + */ > +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); > + > + obj_wasted /= get_maxobj_per_zspage(class->size, > + class->pages_per_zspage); I don't think we need division and make it simple. return obj_wasted >= get_maxobj_per_zspage > + return obj_wasted; > +} > + > static unsigned long __zs_compact(struct zs_pool *pool, > struct size_class *class) > { > @@ -1695,6 +1717,9 @@ 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; > > -- > 2.4.2.387.gf86f31a > -- Kind regards, Minchan Kim From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f179.google.com (mail-pd0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id BF36A6B0038 for ; Tue, 16 Jun 2015 10:19:23 -0400 (EDT) Received: by pdjn11 with SMTP id n11so15530224pdj.0 for ; Tue, 16 Jun 2015 07:19:23 -0700 (PDT) Received: from mail-pa0-x22d.google.com (mail-pa0-x22d.google.com. [2607:f8b0:400e:c03::22d]) by mx.google.com with ESMTPS id sn2si1560071pac.206.2015.06.16.07.19.22 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Jun 2015 07:19:22 -0700 (PDT) Received: by pacyx8 with SMTP id yx8so13781565pac.2 for ; Tue, 16 Jun 2015 07:19:22 -0700 (PDT) Date: Tue, 16 Jun 2015 23:19:14 +0900 From: Minchan Kim Subject: Re: [RFC][PATCHv2 5/8] zsmalloc: introduce zs_can_compact() function Message-ID: <20150616141914.GC31387@blaptop> References: <1433505838-23058-1-git-send-email-sergey.senozhatsky@gmail.com> <1433505838-23058-6-git-send-email-sergey.senozhatsky@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1433505838-23058-6-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 Fri, Jun 05, 2015 at 09:03:55PM +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, > -- estimated number of pages that will be freed > > [..] > class-3072 objs:24652 inuse:24628 maxobjs-per-page:4 pages-tofree:6 Please use clear term. We have been used zspage as cluster of pages. maxobjs-per-zspage:4 And say what is pages-per-zspage for each class. then, write how you calculate it for easy reviewing. * class-3072 * pages-per-zspage: 3 * maxobjs-per-zspage = 4 In your example, allocated obj = 24652 and inuse obj = 24628 so 24652 - 24628 = 24 = 4(ie, maxobjs-per-zspage) * 6 so we can save 6 zspage. A zspage includes 3 pages so we can save 3 * 6 = 18 pages via compaction. > class-3072 objs:24648 inuse:24628 maxobjs-per-page:4 pages-tofree:5 > class-3072 objs:24644 inuse:24628 maxobjs-per-page:4 pages-tofree:4 > class-3072 objs:24640 inuse:24628 maxobjs-per-page:4 pages-tofree:3 > class-3072 objs:24636 inuse:24628 maxobjs-per-page:4 pages-tofree:2 > class-3072 objs:24632 inuse:24628 maxobjs-per-page:4 pages-tofree:1 > class-2720 objs:17970 inuse:17966 maxobjs-per-page:3 pages-tofree:1 > class-2720 objs:17967 inuse:17966 maxobjs-per-page:3 pages-tofree:0 > class-2720: Compaction is useless > class-2448 objs:7680 inuse:7674 maxobjs-per-page:5 pages-tofree:1 > class-2336 objs:13510 inuse:13500 maxobjs-per-page:7 pages-tofree:1 > class-2336 objs:13503 inuse:13500 maxobjs-per-page:7 pages-tofree:0 > class-2336: Compaction is useless > class-1808 objs:1161 inuse:1154 maxobjs-per-page:9 pages-tofree:0 > class-1808: Compaction is useless > class-1744 objs:2135 inuse:2131 maxobjs-per-page:7 pages-tofree:0 > class-1744: Compaction is useless > class-1536 objs:1328 inuse:1323 maxobjs-per-page:8 pages-tofree:0 > class-1536: Compaction is useless > class-1488 objs:8855 inuse:8847 maxobjs-per-page:11 pages-tofree:0 > class-1488: Compaction is useless > class-1360 objs:14880 inuse:14878 maxobjs-per-page:3 pages-tofree:0 > class-1360: Compaction is useless > class-1248 objs:3588 inuse:3577 maxobjs-per-page:13 pages-tofree:0 > class-1248: Compaction is useless > class-1216 objs:3380 inuse:3372 maxobjs-per-page:10 pages-tofree:0 > class-1216: Compaction is useless > class-1168 objs:3416 inuse:3401 maxobjs-per-page:7 pages-tofree:2 > class-1168 objs:3409 inuse:3401 maxobjs-per-page:7 pages-tofree:1 > class-1104 objs:605 inuse:599 maxobjs-per-page:11 pages-tofree:0 > class-1104: Compaction is useless > [..] > > Every "Compaction is useless" indicates that we saved some CPU cycles. > > class-1104 has > 605 object allocated > 599 objects used > 11 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 here, 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 0453347..5d8f1d4 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1682,6 +1682,28 @@ 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 empty at least one page. free at least one zspage > + * > + * Should be called under class->lock > + */ > +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); > + > + obj_wasted /= get_maxobj_per_zspage(class->size, > + class->pages_per_zspage); I don't think we need division and make it simple. return obj_wasted >= get_maxobj_per_zspage > + return obj_wasted; > +} > + > static unsigned long __zs_compact(struct zs_pool *pool, > struct size_class *class) > { > @@ -1695,6 +1717,9 @@ 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; > > -- > 2.4.2.387.gf86f31a > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org