Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753005Ab1BVBxo (ORCPT ); Mon, 21 Feb 2011 20:53:44 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.141]:38552 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752098Ab1BVBxn (ORCPT ); Mon, 21 Feb 2011 20:53:43 -0500 Subject: [PATCH 1/5] pagewalk: only split huge pages when necessary To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Michael J Wolf , Andrea Arcangeli , akpm@osdl.org, Dave Hansen , Mel Gorman From: Dave Hansen Date: Mon, 21 Feb 2011 17:53:39 -0800 References: <20110222015338.309727CA@kernel> In-Reply-To: <20110222015338.309727CA@kernel> Message-Id: <20110222015339.0C9A2212@kernel> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5463 Lines: 146 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. Acked-by: Mel Gorman 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 2011-02-14 09:59:42.438543522 -0800 +++ linux-2.6.git-dave/fs/proc/task_mmu.c 2011-02-14 09:59:42.458544115 -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 2011-02-14 09:59:42.442543640 -0800 +++ linux-2.6.git-dave/include/linux/mm.h 2011-02-14 09:59:42.458544115 -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 2011-02-14 09:59:42.446543758 -0800 +++ linux-2.6.git-dave/mm/memcontrol.c 2011-02-14 09:59:42.462544233 -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++); 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 2011-02-14 09:59:42.450543877 -0800 +++ linux-2.6.git-dave/mm/pagewalk.c 2011-02-14 09:59:42.466544351 -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); _ -- 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/