Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751765AbaB0Txz (ORCPT ); Thu, 27 Feb 2014 14:53:55 -0500 Received: from mga09.intel.com ([134.134.136.24]:21588 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107AbaB0Txy (ORCPT ); Thu, 27 Feb 2014 14:53:54 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,556,1389772800"; d="scan'208";a="463644397" From: "Kirill A. Shutemov" To: Linus Torvalds , Andrew Morton , Mel Gorman , Rik van Riel Cc: Andi Kleen , Matthew Wilcox , Dave Hansen , Alexander Viro , Dave Chinner , Ning Qu , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Subject: [PATCHv3 1/2] mm: introduce vm_ops->map_pages() Date: Thu, 27 Feb 2014 21:53:46 +0200 Message-Id: <1393530827-25450-2-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 1.9.0 In-Reply-To: <1393530827-25450-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1393530827-25450-1-git-send-email-kirill.shutemov@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The patch introduces new vm_ops callback ->map_pages() and uses it for mapping easy accessible pages around fault address. On read page fault, if filesystem provides ->map_pages(), we try to map up to FAULT_AROUND_PAGES pages around page fault address in hope to reduce number of minor page faults. We call ->map_pages first and use ->fault() as fallback if page by the offset is not ready to be mapped (cold page cache or something). Signed-off-by: Kirill A. Shutemov --- Documentation/filesystems/Locking | 10 ++++++ include/linux/mm.h | 8 +++++ mm/memory.c | 67 +++++++++++++++++++++++++++++++++++++-- 3 files changed, 82 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index 5b0c083d7c0e..767930f04a12 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -525,6 +525,7 @@ locking rules: open: yes close: yes fault: yes can return with page locked +map_pages: yes page_mkwrite: yes can return with page locked access: yes @@ -536,6 +537,15 @@ the page, then ensure it is not already truncated (the page lock will block subsequent truncate), and then return with VM_FAULT_LOCKED, and the page locked. The VM will unlock the page. + ->map_pages() is called when VM asks to map easy accessible pages. +Filesystem should find and map pages associated with offsets from "pgoff" +till "max_pgoff". ->map_pages() is called with page table locked and must +not block. If it's not possible to reach a page without blocking, +filesystem should skip it. Filesystem should use do_set_pte() to setup +page table entry. Pointer to entry associated with offset "pgoff" is +passed in "pte" field in vm_fault structure. Pointers to entries for other +offsets should be calculated relative to "pte". + ->page_mkwrite() is called when a previously read-only pte is about to become writeable. The filesystem again must ensure that there are no truncate/invalidate races, and then return with the page locked. If diff --git a/include/linux/mm.h b/include/linux/mm.h index f28f46eade6a..aed92cb17127 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -210,6 +210,10 @@ struct vm_fault { * is set (which is also implied by * VM_FAULT_ERROR). */ + /* for ->map_pages() only */ + pgoff_t max_pgoff; /* map pages for offset from pgoff till + * max_pgoff inclusive */ + pte_t *pte; /* pte entry associated with ->pgoff */ }; /* @@ -221,6 +225,7 @@ struct vm_operations_struct { void (*open)(struct vm_area_struct * area); void (*close)(struct vm_area_struct * area); int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf); + void (*map_pages)(struct vm_area_struct *vma, struct vm_fault *vmf); /* notification that a previously read-only page is about to become * writable, if an error is returned it will cause a SIGBUS */ @@ -571,6 +576,9 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) pte = pte_mkwrite(pte); return pte; } + +void do_set_pte(struct vm_area_struct *vma, unsigned long address, + struct page *page, pte_t *pte, bool write, bool anon); #endif /* diff --git a/mm/memory.c b/mm/memory.c index 7f52c46ef1e1..3f17a60e817f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3318,7 +3318,8 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, return ret; } -static void do_set_pte(struct vm_area_struct *vma, unsigned long address, + +void do_set_pte(struct vm_area_struct *vma, unsigned long address, struct page *page, pte_t *pte, bool write, bool anon) { pte_t entry; @@ -3342,6 +3343,52 @@ static void do_set_pte(struct vm_area_struct *vma, unsigned long address, update_mmu_cache(vma, address, pte); } +#define FAULT_AROUND_ORDER 4 +#define FAULT_AROUND_PAGES (1UL << FAULT_AROUND_ORDER) +#define FAULT_AROUND_MASK ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1) + +static void do_fault_around(struct vm_area_struct *vma, unsigned long address, + pte_t *pte, pgoff_t pgoff, unsigned int flags) +{ + unsigned long start_addr; + pgoff_t max_pgoff; + struct vm_fault vmf; + int off; + + BUILD_BUG_ON(FAULT_AROUND_PAGES > PTRS_PER_PTE); + + start_addr = max(address & FAULT_AROUND_MASK, vma->vm_start); + off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1); + pte -= off; + pgoff -= off; + + /* + * max_pgoff is either end of page table or end of vma + * or FAULT_AROUND_PAGES from pgoff, depending what is neast. + */ + max_pgoff = pgoff - ((start_addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) + + PTRS_PER_PTE - 1; + max_pgoff = min3(max_pgoff, vma_pages(vma) + vma->vm_pgoff - 1, + pgoff + FAULT_AROUND_PAGES - 1); + + /* Check if it makes any sense to call ->map_pages */ + while (!pte_none(*pte)) { + if (++pgoff > max_pgoff) + return; + start_addr += PAGE_SIZE; + if (start_addr >= vma->vm_end) + return; + pte++; + } + + vmf.virtual_address = (void __user *) start_addr; + vmf.pte = pte; + vmf.pgoff = pgoff; + vmf.max_pgoff = max_pgoff; + vmf.flags = flags; + vma->vm_ops->map_pages(vma, &vmf); +} + static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, pmd_t *pmd, pgoff_t pgoff, unsigned int flags, pte_t orig_pte) @@ -3349,7 +3396,20 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, struct page *fault_page; spinlock_t *ptl; pte_t *pte; - int ret; + int ret = 0; + + /* + * Let's call ->map_pages() first and use ->fault() as fallback + * if page by the offset is not ready to be mapped (cold cache or + * something). + */ + if (vma->vm_ops->map_pages) { + pte = pte_offset_map_lock(mm, pmd, address, &ptl); + do_fault_around(vma, address, pte, pgoff, flags); + if (!pte_same(*pte, orig_pte)) + goto unlock_out; + pte_unmap_unlock(pte, ptl); + } ret = __do_fault(vma, address, pgoff, flags, &fault_page); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) @@ -3363,8 +3423,9 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, return ret; } do_set_pte(vma, address, fault_page, pte, false, false); - pte_unmap_unlock(pte, ptl); unlock_page(fault_page); +unlock_out: + pte_unmap_unlock(pte, ptl); return ret; } -- 1.9.0 -- 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/