Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751323AbcDRBCk (ORCPT ); Sun, 17 Apr 2016 21:02:40 -0400 Received: from mail-pa0-f67.google.com ([209.85.220.67]:34232 "EHLO mail-pa0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750997AbcDRBCj (ORCPT ); Sun, 17 Apr 2016 21:02:39 -0400 Date: Mon, 18 Apr 2016 10:04:08 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, jlayton@poochiereds.net, bfields@fieldses.org, Vlastimil Babka , Joonsoo Kim , koct9i@gmail.com, aquini@redhat.com, virtualization@lists.linux-foundation.org, Mel Gorman , Hugh Dickins , Sergey Senozhatsky , Rik van Riel , rknize@motorola.com, Gioh Kim , Sangseok Lee , Chan Gyun Jeong , Al Viro , YiPing Xu Subject: Re: [PATCH v3 11/16] zsmalloc: separate free_zspage from putback_zspage Message-ID: <20160418010408.GB5882@swordfish> References: <1459321935-3655-1-git-send-email-minchan@kernel.org> <1459321935-3655-12-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1459321935-3655-12-git-send-email-minchan@kernel.org> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2177 Lines: 80 Hello Minchan, On (03/30/16 16:12), Minchan Kim wrote: [..] > @@ -1835,23 +1827,31 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class) > if (!migrate_zspage(pool, class, &cc)) > break; > > - putback_zspage(pool, class, dst_page); > + VM_BUG_ON_PAGE(putback_zspage(pool, class, > + dst_page) == ZS_EMPTY, dst_page); can this VM_BUG_ON_PAGE() condition ever be true? > } > /* Stop if we couldn't find slot */ > if (dst_page == NULL) > break; > - putback_zspage(pool, class, dst_page); > - if (putback_zspage(pool, class, src_page) == ZS_EMPTY) > + VM_BUG_ON_PAGE(putback_zspage(pool, class, > + dst_page) == ZS_EMPTY, dst_page); hm... this VM_BUG_ON_PAGE(dst_page) is sort of confusing. under what circumstances it can be true? a minor nit, it took me some time (need some coffee I guess) to correctly parse this macro wrapper VM_BUG_ON_PAGE(putback_zspage(pool, class, dst_page) == ZS_EMPTY, dst_page); may be do it like: fullness = putback_zspage(pool, class, dst_page); VM_BUG_ON_PAGE(fullness == ZS_EMPTY, dst_page); well, if we want to VM_BUG_ON_PAGE() at all. there haven't been any problems with compaction, is there any specific reason these macros were added? > + if (putback_zspage(pool, class, src_page) == ZS_EMPTY) { > pool->stats.pages_compacted += class->pages_per_zspage; > - spin_unlock(&class->lock); > + spin_unlock(&class->lock); > + free_zspage(pool, class, src_page); do we really need to free_zspage() out of class->lock? wouldn't something like this if (putback_zspage(pool, class, src_page) == ZS_EMPTY) { pool->stats.pages_compacted += class->pages_per_zspage; free_zspage(pool, class, src_page); } spin_unlock(&class->lock); be simpler? besides, free_zspage() now updates class stats out of class lock, not critical but still. -ss > + } else { > + spin_unlock(&class->lock); > + } > + > cond_resched(); > spin_lock(&class->lock); > } > > if (src_page) > - putback_zspage(pool, class, src_page); > + VM_BUG_ON_PAGE(putback_zspage(pool, class, > + src_page) == ZS_EMPTY, src_page); > > spin_unlock(&class->lock); > }