From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753529AbbJTVhF (ORCPT ); Tue, 20 Oct 2015 17:37:05 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:42261 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753034AbbJTVgw (ORCPT ); Tue, 20 Oct 2015 17:36:52 -0400 Date: Tue, 20 Oct 2015 14:36:51 -0700 From: Andrew Morton To: Minchan Kim Cc: "Kirill A. Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Rik van Riel , Mel Gorman , Michal Hocko , Johannes Weiner , Vlastimil Babka Subject: Re: [PATCH 0/5] MADV_FREE refactoring and fix KSM page Message-Id: <20151020143651.64ce2c459cda168c714caf93@linux-foundation.org> In-Reply-To: <20151020072109.GD2941@bbox> References: <1445236307-895-1-git-send-email-minchan@kernel.org> <20151019100150.GA5194@bbox> <20151020072109.GD2941@bbox> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 Oct 2015 16:21:09 +0900 Minchan Kim wrote: > > I reviewed THP refcount redesign patch and It seems below patch fixes > MADV_FREE problem. It works well for hours. > > >From 104a0940b4c0f97e61de9fee0fd602926ff28312 Mon Sep 17 00:00:00 2001 > From: Minchan Kim > Date: Tue, 20 Oct 2015 16:00:52 +0900 > Subject: [PATCH] mm: mark head page dirty in split_huge_page > > In thp split in old THP refcount, we mappped all of pages > (ie, head + tails) to pte_mkdirty and mark PG_flags to every > tail pages. > > But with THP refcount redesign, we can lose dirty bit in page table > and PG_dirty for head page if we want to free the THP page using > migration_entry. > > It ends up discarding head page by madvise_free suddenly. > This patch fixes it by mark the head page PG_dirty when VM splits > the THP page. > > Signed-off-by: Minchan Kim > --- > mm/huge_memory.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index adccfb48ce57..7fbbd42554a1 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3258,6 +3258,7 @@ static void __split_huge_page(struct page *page, struct list_head *list) > atomic_sub(tail_mapcount, &head->_count); > > ClearPageCompound(head); > + SetPageDirty(head); > spin_unlock_irq(&zone->lru_lock); > > unfreeze_page(page_anon_vma(head), head); This appears to be a bugfix against Kirill's "thp: reintroduce split_huge_page()"? Yes, __split_huge_page() is marking the tail pages dirty but forgot about the head page You say "we can lose dirty bit in page table" but I don't see how the above patch fixes that? Why does __split_huge_page() unconditionally mark the pages dirty, btw? Is it because the THP page was known to be dirty? If so, the head page already had PG_dirty, so this patch doesn't do anything. freeze_page(), unfreeze_page() and their callees desperately need some description of what they're doing. Kirill, could you cook somethnig up please?