From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753781AbbJTWpX (ORCPT ); Tue, 20 Oct 2015 18:45:23 -0400 Received: from mail-wi0-f179.google.com ([209.85.212.179]:36842 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754202AbbJTWn4 (ORCPT ); Tue, 20 Oct 2015 18:43:56 -0400 Date: Wed, 21 Oct 2015 01:43:53 +0300 From: "Kirill A. Shutemov" To: Andrew Morton Cc: Minchan Kim , 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: <20151020224353.GA10597@node.shutemov.name> References: <1445236307-895-1-git-send-email-minchan@kernel.org> <20151019100150.GA5194@bbox> <20151020072109.GD2941@bbox> <20151020143651.64ce2c459cda168c714caf93@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151020143651.64ce2c459cda168c714caf93@linux-foundation.org> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 20, 2015 at 02:36:51PM -0700, Andrew Morton wrote: > 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); Sorry, I've missed the email at first. > 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? I think the problem is in unfreeze_page_vma(), where I missed dirtying pte. > Why does __split_huge_page() unconditionally mark the pages dirty, btw? > Is it because the THP page was known to be dirty? THP doesn't have backing storage and cannot be swapped out without splitting, therefore always dirty. (huge zero page is exception, I guess). > If so, the head page already had PG_dirty, so this patch doesn't do > anything. PG_dirty appears on struct page as result of transferring from dirty bit in page tables. There's no guarantee that it's happened. > freeze_page(), unfreeze_page() and their callees desperately need some > description of what they're doing. Kirill, could you cook somethnig up > please? Minchan, could you test patch below instead? diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 86924cc34bac..ea1f3805afa3 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3115,7 +3115,7 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page, entry = pte_mkold(mk_pte(page, vma->vm_page_prot)); if (is_write_migration_entry(swp_entry)) - entry = maybe_mkwrite(entry, vma); + entry = maybe_mkwrite(pte_mkdirty(entry), vma); flush_dcache_page(page); set_pte_at(vma->vm_mm, address, pte + i, entry); -- Kirill A. Shutemov