From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 807546B0289 for ; Tue, 24 Oct 2017 11:30:41 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id k15so11932932wrc.1 for ; Tue, 24 Oct 2017 08:30:41 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id u54si389508wrf.243.2017.10.24.08.30.38 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 24 Oct 2017 08:30:38 -0700 (PDT) Date: Tue, 24 Oct 2017 17:30:37 +0200 From: Michal Hocko Subject: Re: [PATCH -mm] mm, swap: Fix false error message in __swp_swapcount() Message-ID: <20171024153037.gjemriarubzoqai5@dhcp22.suse.cz> References: <20171024024700.23679-1-ying.huang@intel.com> <20171024083809.lrw23yumkassclgm@dhcp22.suse.cz> <87vaj4poff.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87vaj4poff.fsf@yhuang-dev.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Huang, Ying" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tim Chen , Minchan Kim , stable@vger.kernel.org, Christian Kujau On Tue 24-10-17 23:15:32, Huang, Ying wrote: > Hi, Michal, > > Michal Hocko writes: > > > On Tue 24-10-17 10:47:00, Huang, Ying wrote: > >> From: Ying Huang > >> > >> __swp_swapcount() is used in __read_swap_cache_async(). Where the > >> invalid swap entry (offset > max) may be supplied during swap > >> readahead. But __swp_swapcount() will print error message for these > >> expected invalid swap entry as below, which will make the users > >> confusing. > > ^^ > > confused... And I have to admit this changelog has left me confused as > > well. What is an invalid swap entry in the readahead? Ohh, let me > > re-real Fixes: commit. It didn't really help "We can avoid needlessly > > allocating page for swap slots that are not used by anyone. No pages > > have to be read in for these slots." > > > > Could you be more specific about when and how this happens please? > > Sorry for confusing. > > When page fault occurs for a swap entry, the original swap readahead > (not new VMA base swap readahead) may readahead several swap entries > after the fault swap entry. The readahead algorithm calculates some of > the swap entries to readahead via increasing the offset of the fault > swap entry without checking whether they are beyond the end of the swap > device and it rely on the __swp_swapcount() and swapcache_prepare() to > check it. Although __swp_swapcount() checks for the swap entry passed > in, it will complain with error message for the expected invalid swap > entry. This makes the end user confusing. > > Is this a little clearer. yes, this makes more sense (modulo the same typo ;)). Can you make this information into the changelog please? Thanks. -- Michal Hocko SUSE Labs -- 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