From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934844AbdBQQLW (ORCPT ); Fri, 17 Feb 2017 11:11:22 -0500 Received: from gum.cmpxchg.org ([85.214.110.215]:35826 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934209AbdBQQLT (ORCPT ); Fri, 17 Feb 2017 11:11:19 -0500 Date: Fri, 17 Feb 2017 11:11:05 -0500 From: Johannes Weiner To: Minchan Kim Cc: Shaohua Li , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kernel-team@fb.com, mhocko@suse.com, hughd@google.com, riel@redhat.com, mgorman@techsingularity.net, akpm@linux-foundation.org Subject: Re: [PATCH V3 3/7] mm: reclaim MADV_FREE pages Message-ID: <20170217161105.GB23735@cmpxchg.org> References: <20170216184018.GC20791@cmpxchg.org> <20170217002717.GA93163@shli-mbp.local> <20170217054555.GB3653@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170217054555.GB3653@bbox> User-Agent: Mutt/1.7.2 (2016-11-26) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Minchan, On Fri, Feb 17, 2017 at 02:45:55PM +0900, Minchan Kim wrote: > On Thu, Feb 16, 2017 at 04:27:18PM -0800, Shaohua Li wrote: > > On Thu, Feb 16, 2017 at 01:40:18PM -0500, Johannes Weiner wrote: > > > On Tue, Feb 14, 2017 at 11:36:09AM -0800, Shaohua Li wrote: > > > > @@ -1419,11 +1419,18 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > > > > VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page), > > > > page); > > > > > > > > - if (!PageDirty(page) && (flags & TTU_LZFREE)) { > > > > - /* It's a freeable page by MADV_FREE */ > > > > - dec_mm_counter(mm, MM_ANONPAGES); > > > > - rp->lazyfreed++; > > > > - goto discard; > > > > + if (flags & TTU_LZFREE) { > > > > + if (!PageDirty(page)) { > > > > + /* It's a freeable page by MADV_FREE */ > > > > + dec_mm_counter(mm, MM_ANONPAGES); > > > > + rp->lazyfreed++; > > > > + goto discard; > > > > + } else { > > > > + set_pte_at(mm, address, pvmw.pte, pteval); > > > > + ret = SWAP_FAIL; > > > > + page_vma_mapped_walk_done(&pvmw); > > > > + break; > > > > + } > > > > > > I don't understand why we need the TTU_LZFREE bit in general. More on > > > that below at the callsite. > > > > Sounds useless flag, don't see any reason we shouldn't free the MADV_FREE page > > in places other than reclaim. Looks TTU_UNMAP is useless too.. > > Agree on TTU_UNMAP but for example, THP split doesn't mean free lazyfree pages, > I think. Anon THP splitting uses the migration branch, so we should be fine.