Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756046Ab1BJLLx (ORCPT ); Thu, 10 Feb 2011 06:11:53 -0500 Received: from gir.skynet.ie ([193.1.99.77]:43324 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751664Ab1BJLLw (ORCPT ); Thu, 10 Feb 2011 06:11:52 -0500 Date: Thu, 10 Feb 2011 11:11:25 +0000 From: Mel Gorman To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michael J Wolf , Andrea Arcangeli Subject: Re: [PATCH 1/5] pagewalk: only split huge pages when necessary Message-ID: <20110210111125.GC17873@csn.ul.ie> References: <20110209195406.B9F23C9F@kernel> <20110209195407.2CE28EA0@kernel> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20110209195407.2CE28EA0@kernel> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6013 Lines: 155 On Wed, Feb 09, 2011 at 11:54:07AM -0800, Dave Hansen wrote: > > v2 - rework if() block, and remove now redundant split_huge_page() > > Right now, if a mm_walk has either ->pte_entry or ->pmd_entry > set, it will unconditionally split any transparent huge pages > it runs in to. In practice, that means that anyone doing a > > cat /proc/$pid/smaps > > will unconditionally break down every huge page in the process > and depend on khugepaged to re-collapse it later. This is > fairly suboptimal. > > This patch changes that behavior. It teaches each ->pmd_entry > handler (there are five) that they must break down the THPs > themselves. Also, the _generic_ code will never break down > a THP unless a ->pte_entry handler is actually set. > > This means that the ->pmd_entry handlers can now choose to > deal with THPs without breaking them down. > > Signed-off-by: Dave Hansen > --- > > linux-2.6.git-dave/fs/proc/task_mmu.c | 6 ++++++ > linux-2.6.git-dave/include/linux/mm.h | 3 +++ > linux-2.6.git-dave/mm/memcontrol.c | 5 +++-- > linux-2.6.git-dave/mm/pagewalk.c | 24 ++++++++++++++++++++---- > 4 files changed, 32 insertions(+), 6 deletions(-) > > diff -puN fs/proc/task_mmu.c~pagewalk-dont-always-split-thp fs/proc/task_mmu.c > --- linux-2.6.git/fs/proc/task_mmu.c~pagewalk-dont-always-split-thp 2011-02-09 11:41:42.299558364 -0800 > +++ linux-2.6.git-dave/fs/proc/task_mmu.c 2011-02-09 11:41:42.319558349 -0800 > @@ -343,6 +343,8 @@ static int smaps_pte_range(pmd_t *pmd, u > struct page *page; > int mapcount; > > + split_huge_page_pmd(walk->mm, pmd); > + > pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > for (; addr != end; pte++, addr += PAGE_SIZE) { > ptent = *pte; > @@ -467,6 +469,8 @@ static int clear_refs_pte_range(pmd_t *p > spinlock_t *ptl; > struct page *page; > > + split_huge_page_pmd(walk->mm, pmd); > + > pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > for (; addr != end; pte++, addr += PAGE_SIZE) { > ptent = *pte; > @@ -623,6 +627,8 @@ static int pagemap_pte_range(pmd_t *pmd, > pte_t *pte; > int err = 0; > > + split_huge_page_pmd(walk->mm, pmd); > + > /* find the first VMA at or above 'addr' */ > vma = find_vma(walk->mm, addr); > for (; addr != end; addr += PAGE_SIZE) { > diff -puN include/linux/mm.h~pagewalk-dont-always-split-thp include/linux/mm.h > --- linux-2.6.git/include/linux/mm.h~pagewalk-dont-always-split-thp 2011-02-09 11:41:42.303558361 -0800 > +++ linux-2.6.git-dave/include/linux/mm.h 2011-02-09 11:41:42.323558346 -0800 > @@ -899,6 +899,9 @@ unsigned long unmap_vmas(struct mmu_gath > * @pgd_entry: if set, called for each non-empty PGD (top-level) entry > * @pud_entry: if set, called for each non-empty PUD (2nd-level) entry > * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry > + * this handler is required to be able to handle > + * pmd_trans_huge() pmds. They may simply choose to > + * split_huge_page() instead of handling it explicitly. > * @pte_entry: if set, called for each non-empty PTE (4th-level) entry > * @pte_hole: if set, called for each hole at all levels > * @hugetlb_entry: if set, called for each hugetlb entry > diff -puN mm/memcontrol.c~pagewalk-dont-always-split-thp mm/memcontrol.c > --- linux-2.6.git/mm/memcontrol.c~pagewalk-dont-always-split-thp 2011-02-09 11:41:42.311558355 -0800 > +++ linux-2.6.git-dave/mm/memcontrol.c 2011-02-09 11:41:42.327558343 -0800 > @@ -4737,7 +4737,8 @@ static int mem_cgroup_count_precharge_pt > pte_t *pte; > spinlock_t *ptl; > > - VM_BUG_ON(pmd_trans_huge(*pmd)); > + split_huge_page_pmd(walk->mm, pmd); > + > pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > for (; addr != end; pte++, addr += PAGE_SIZE) > if (is_target_pte_for_mc(vma, addr, *pte, NULL)) > @@ -4899,8 +4900,8 @@ static int mem_cgroup_move_charge_pte_ra > pte_t *pte; > spinlock_t *ptl; > > + split_huge_page_pmd(walk->mm, pmd); > retry: > - VM_BUG_ON(pmd_trans_huge(*pmd)); > pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > for (; addr != end; addr += PAGE_SIZE) { > pte_t ptent = *(pte++); Before we goto this retry, there is at a cond_resched(). Just to confirm, we are depending on mmap_sem to prevent khugepaged promoting this back to a hugepage, right? I don't see a problem with that but I want to be sure. > diff -puN mm/pagewalk.c~pagewalk-dont-always-split-thp mm/pagewalk.c > --- linux-2.6.git/mm/pagewalk.c~pagewalk-dont-always-split-thp 2011-02-09 11:41:42.315558352 -0800 > +++ linux-2.6.git-dave/mm/pagewalk.c 2011-02-09 11:41:42.331558340 -0800 > @@ -33,19 +33,35 @@ static int walk_pmd_range(pud_t *pud, un > > pmd = pmd_offset(pud, addr); > do { > + again: > next = pmd_addr_end(addr, end); > - split_huge_page_pmd(walk->mm, pmd); > - if (pmd_none_or_clear_bad(pmd)) { > + if (pmd_none(*pmd)) { > if (walk->pte_hole) > err = walk->pte_hole(addr, next, walk); > if (err) > break; > continue; > } > + /* > + * This implies that each ->pmd_entry() handler > + * needs to know about pmd_trans_huge() pmds > + */ > if (walk->pmd_entry) > err = walk->pmd_entry(pmd, addr, next, walk); > - if (!err && walk->pte_entry) > - err = walk_pte_range(pmd, addr, next, walk); > + if (err) > + break; > + > + /* > + * Check this here so we only break down trans_huge > + * pages when we _need_ to > + */ > + if (!walk->pte_entry) > + continue; > + > + split_huge_page_pmd(walk->mm, pmd); > + if (pmd_none_or_clear_bad(pmd)) > + goto again; > + err = walk_pte_range(pmd, addr, next, walk); > if (err) > break; > } while (pmd++, addr = next, addr != end); -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/