From 033193275b3ffcfe7f3fde7b569f3d207f6cd6a0 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Tue, 22 Mar 2011 16:32:56 -0700 Subject: [PATCH] pagewalk: only split huge pages when necessary 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. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Dave Hansen Acked-by: Mel Gorman Acked-by: David Rientjes Reviewed-by: Eric B Munson Tested-by: Eric B Munson Cc: Michael J Wolf Cc: Andrea Arcangeli Cc: Johannes Weiner Cc: Matt Mackall Cc: Jeremy Fitzhardinge Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/task_mmu.c | 6 ++++++ include/linux/mm.h | 3 +++ mm/memcontrol.c | 5 +++-- mm/pagewalk.c | 24 ++++++++++++++++++++---- 4 files changed, 32 insertions(+), 6 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 60b914860f8..78fd3621f56 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -343,6 +343,8 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, 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 *pmd, unsigned long addr, 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, unsigned long addr, unsigned long end, 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 --git a/include/linux/mm.h b/include/linux/mm.h index 901435e3a9a..294104e0891 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -914,6 +914,9 @@ unsigned long unmap_vmas(struct mmu_gather **tlb, * @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 --git a/mm/memcontrol.c b/mm/memcontrol.c index 9e0f05efd11..e1ee6ad9c97 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4763,7 +4763,8 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd, 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)) @@ -4925,8 +4926,8 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd, 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 --git a/mm/pagewalk.c b/mm/pagewalk.c index 7cfa6ae0230..c3450d53361 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -33,19 +33,35 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, 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); -- 2.20.1