From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [PATCH v3 11/16] zsmalloc: separate free_zspage from putback_zspage Date: Tue, 19 Apr 2016 16:51:18 +0900 Message-ID: <20160419075118.GD18448__3855.17194304175$1461052244$gmane$org@bbox> References: <1459321935-3655-1-git-send-email-minchan@kernel.org> <1459321935-3655-12-git-send-email-minchan@kernel.org> <20160418010408.GB5882@swordfish> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160418010408.GB5882@swordfish> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Sergey Senozhatsky Cc: Rik van Riel , YiPing Xu , aquini@redhat.com, rknize@motorola.com, Sergey Senozhatsky , Chan Gyun Jeong , Hugh Dickins , linux-kernel@vger.kernel.org, Al Viro , virtualization@lists.linux-foundation.org, bfields@fieldses.org, linux-mm@kvack.org, Gioh Kim , koct9i@gmail.com, Sangseok Lee , Joonsoo Kim , Andrew Morton , jlayton@poochiereds.net, Vlastimil Babka , Mel Gorman List-Id: virtualization@lists.linuxfoundation.org Hi Sergey, On Mon, Apr 18, 2016 at 10:04:08AM +0900, Sergey Senozhatsky wrote: > 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? I guess it is remained thing after I rebased to catch any mistake. But I'm heavily chainging this part. Please review next version instead of this after a few days. :) > > > } > > /* 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? The reason I did out of class->lock is deadlock between page_lock and class->lock with upcoming page migration. However, as I said, I'm now heavily changing the part. :) > > 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); > > }