Messages in this thread Patch in this message | | | Subject | [PATCH] mm: tracking dirty pages -v6 | From | Peter Zijlstra <> | Date | Thu, 08 Jun 2006 14:44:14 +0200 |
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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
People expressed the need to track dirty pages in shared mappings.
Linus outlined the general idea of doing that through making clean writable pages write-protected and taking the write fault.
This patch does exactly that, it makes pages in a shared writable mapping write-protected. On write-fault the pages are marked dirty and made writable. When the pages get synced with their backing store, the write-protection is re-instated.
It survives a simple test and shows the dirty pages in /proc/vmstat.
Changes in -v6
- make page_mkclean_one() modify the pte more like change_pte_range() (suggested by Christoph Lameter) - made is_shared_writable() take vm_flags, it now resembles is_cow_mapping(). - fixed the mprotect() bug (spotted by Hugh Dickins) - hopefully fixed the tiresome issue of do_mmap_pgoff() trampling on driver specific vm_page_prot settings (spotted by Hugh Dickins)
This does add the requirement that f_op->mmap() may not 'reset' vm_page_prot from vm_flags. I checked all in-kernel users and non seem to do this.
- made a new version of the page_mkwrite() patch to go on top of all this. This so that Linus could merge this very early on in 2.6.18.
Changes in -v5
- rename page_wrprotect() to page_mkclean() (suggested by Nick Piggin) - added comment to test_clear_page_dirty() (Andrew Morton) - cleanup page_wrprotect() (Andrew Morton) - renamed VM_SharedWritable() to is_shared_writable() - fs/buffers.c try_to_free_buffers(): remove clear_page_dirty() from under ->private_lock. This seems to be save, since ->private_lock is used to serialize access to the buffers, not the page itself. - rebased on top of David Howells' page_mkwrite() patch.
Changes in -v4:
- small cleanup as suggested by Christoph Lameter.
Changes in -v3:
- move set_page_dirty() outside pte lock (suggested by Christoph Lameter)
Changes in -v2:
- only wrprotect pages from dirty capable mappings. (Nick Piggin) - move the writefault handling from do_wp_page() into handle_pte_fault(). (Nick Piggin) - revert to the old install_page interface. (Nick Piggin) - also clear the pte dirty bit when we make pages read-only again. (spotted by Rik van Riel) - make page_wrprotect() return the number of reprotected ptes.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
drivers/char/drm/drm_vm.c | 5 ++- fs/buffer.c | 2 - include/linux/mm.h | 5 +++ include/linux/rmap.h | 8 +++++ mm/memory.c | 45 +++++++++++++++++++++++--------- mm/mmap.c | 28 ++++++++++++++++++-- mm/mprotect.c | 14 ++++++++-- mm/page-writeback.c | 13 +++++++-- mm/rmap.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++ 9 files changed, 163 insertions(+), 21 deletions(-)
Index: linux-2.6/include/linux/mm.h =================================================================== --- linux-2.6.orig/include/linux/mm.h 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/include/linux/mm.h 2006-06-08 13:59:37.000000000 +0200 @@ -183,6 +183,11 @@ extern unsigned int kobjsize(const void #define VM_SequentialReadHint(v) ((v)->vm_flags & VM_SEQ_READ) #define VM_RandomReadHint(v) ((v)->vm_flags & VM_RAND_READ) +static inline int is_shared_writable(unsigned int flags) +{ + return (flags & (VM_SHARED|VM_WRITE)) == (VM_SHARED|VM_WRITE); +} + /* * mapping from the currently active vm_flags protection bits (the * low four bits) to a page protection mask.. Index: linux-2.6/mm/memory.c =================================================================== --- linux-2.6.orig/mm/memory.c 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/mm/memory.c 2006-06-08 13:59:37.000000000 +0200 @@ -1445,25 +1445,31 @@ static int do_wp_page(struct mm_struct * { struct page *old_page, *new_page; pte_t entry; - int ret = VM_FAULT_MINOR; + int reuse = 0, ret = VM_FAULT_MINOR; + struct page *dirty_page = NULL; old_page = vm_normal_page(vma, address, orig_pte); if (!old_page) goto gotten; - if (PageAnon(old_page) && !TestSetPageLocked(old_page)) { - int reuse = can_share_swap_page(old_page); + if (vma->vm_flags & VM_SHARED) { + reuse = 1; + dirty_page = old_page; + get_page(dirty_page); + } else if (PageAnon(old_page) && !TestSetPageLocked(old_page)) { + reuse = can_share_swap_page(old_page); unlock_page(old_page); - if (reuse) { - flush_cache_page(vma, address, pte_pfn(orig_pte)); - entry = pte_mkyoung(orig_pte); - entry = maybe_mkwrite(pte_mkdirty(entry), vma); - ptep_set_access_flags(vma, address, page_table, entry, 1); - update_mmu_cache(vma, address, entry); - lazy_mmu_prot_update(entry); - ret |= VM_FAULT_WRITE; - goto unlock; - } + } + + if (reuse) { + flush_cache_page(vma, address, pte_pfn(orig_pte)); + entry = pte_mkyoung(orig_pte); + entry = maybe_mkwrite(pte_mkdirty(entry), vma); + ptep_set_access_flags(vma, address, page_table, entry, 1); + update_mmu_cache(vma, address, entry); + lazy_mmu_prot_update(entry); + ret |= VM_FAULT_WRITE; + goto unlock; } /* @@ -1518,6 +1524,10 @@ gotten: page_cache_release(old_page); unlock: pte_unmap_unlock(page_table, ptl); + if (dirty_page) { + set_page_dirty(dirty_page); + put_page(dirty_page); + } return ret; oom: if (old_page) @@ -2046,6 +2056,7 @@ static int do_no_page(struct mm_struct * unsigned int sequence = 0; int ret = VM_FAULT_MINOR; int anon = 0; + struct page *dirty_page = NULL; pte_unmap(page_table); BUG_ON(vma->vm_flags & VM_PFNMAP); @@ -2127,6 +2138,10 @@ retry: } else { inc_mm_counter(mm, file_rss); page_add_file_rmap(new_page); + if (write_access) { + dirty_page = new_page; + get_page(dirty_page); + } } } else { /* One of our sibling threads was faster, back out. */ @@ -2139,6 +2154,10 @@ retry: lazy_mmu_prot_update(entry); unlock: pte_unmap_unlock(page_table, ptl); + if (dirty_page) { + set_page_dirty(dirty_page); + put_page(dirty_page); + } return ret; oom: page_cache_release(new_page); Index: linux-2.6/mm/mmap.c =================================================================== --- linux-2.6.orig/mm/mmap.c 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/mm/mmap.c 2006-06-08 14:08:04.000000000 +0200 @@ -25,6 +25,7 @@ #include <linux/mount.h> #include <linux/mempolicy.h> #include <linux/rmap.h> +#include <linux/backing-dev.h> #include <asm/uaccess.h> #include <asm/cacheflush.h> @@ -1065,10 +1066,13 @@ munmap_back: vma->vm_start = addr; vma->vm_end = addr + len; vma->vm_flags = vm_flags; - vma->vm_page_prot = protection_map[vm_flags & 0x0f]; + vma->vm_page_prot = protection_map[vm_flags & + (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]; vma->vm_pgoff = pgoff; if (file) { + struct address_space *mapping = NULL; + error = -EINVAL; if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)) goto free_vma; @@ -1080,6 +1084,25 @@ munmap_back: } vma->vm_file = file; get_file(file); + + /* Trap writes to shared writable mappings that have + * dirty page accounting. + * + * f_op->open() - sets the backing_dev_info + * f_op->mmap() - modifies vm_page_prot; but will not reset + * from vm_flags. + * + * Hence between the two calls (here) it is save to modify + * vm_page_prot depending on backing_dev_info capabilities. + * + * shmem_backing_dev_info does have BDI_CAP_NO_ACCT_DIRTY. + */ + if (is_shared_writable(vm_flags)) + mapping = file->f_mapping; + if (mapping && mapping_cap_account_dirty(mapping)) + vma->vm_page_prot = protection_map[vm_flags & + (VM_READ|VM_WRITE|VM_EXEC)]; + error = file->f_op->mmap(file, vma); if (error) goto unmap_and_free_vma; @@ -1921,7 +1944,8 @@ unsigned long do_brk(unsigned long addr, vma->vm_end = addr + len; vma->vm_pgoff = pgoff; vma->vm_flags = flags; - vma->vm_page_prot = protection_map[flags & 0x0f]; + vma->vm_page_prot = protection_map[flags & + (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]; vma_link(mm, vma, prev, rb_link, rb_parent); out: mm->total_vm += len >> PAGE_SHIFT; Index: linux-2.6/mm/mprotect.c =================================================================== --- linux-2.6.orig/mm/mprotect.c 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/mm/mprotect.c 2006-06-08 14:15:24.000000000 +0200 @@ -19,6 +19,7 @@ #include <linux/mempolicy.h> #include <linux/personality.h> #include <linux/syscalls.h> +#include <linux/backing-dev.h> #include <asm/uaccess.h> #include <asm/pgtable.h> @@ -106,6 +107,8 @@ mprotect_fixup(struct vm_area_struct *vm unsigned long oldflags = vma->vm_flags; long nrpages = (end - start) >> PAGE_SHIFT; unsigned long charged = 0; + unsigned int mask; + struct address_space *mapping = NULL; pgprot_t newprot; pgoff_t pgoff; int error; @@ -132,8 +135,6 @@ mprotect_fixup(struct vm_area_struct *vm } } - newprot = protection_map[newflags & 0xf]; - /* * First try to merge with previous and/or next vma. */ @@ -160,6 +161,15 @@ mprotect_fixup(struct vm_area_struct *vm } success: + /* Don't make the VMA automatically writable if it's shared. */ + mask = VM_READ|VM_WRITE|VM_EXEC|VM_SHARED; + if (is_shared_writable(newflags) && vma->vm_file) + mapping = vma->vm_file->f_mapping; + if (mapping && mapping_cap_account_dirty(mapping)) + mask &= ~VM_SHARED; + + newprot = protection_map[newflags & mask]; + /* * vm_flags and vm_page_prot are protected by the mmap_sem * held in write mode. Index: linux-2.6/mm/page-writeback.c =================================================================== --- linux-2.6.orig/mm/page-writeback.c 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/mm/page-writeback.c 2006-06-08 13:59:37.000000000 +0200 @@ -29,6 +29,7 @@ #include <linux/sysctl.h> #include <linux/cpu.h> #include <linux/syscalls.h> +#include <linux/rmap.h> /* * The maximum number of pages to writeout in a single bdflush/kupdate @@ -725,8 +726,14 @@ int test_clear_page_dirty(struct page *p page_index(page), PAGECACHE_TAG_DIRTY); write_unlock_irqrestore(&mapping->tree_lock, flags); - if (mapping_cap_account_dirty(mapping)) + /* + * We can continue to use `mapping' here because the + * page is locked, which pins the address_space + */ + if (mapping_cap_account_dirty(mapping)) { + page_mkclean(page); dec_page_state(nr_dirty); + } return 1; } write_unlock_irqrestore(&mapping->tree_lock, flags); @@ -756,8 +763,10 @@ int clear_page_dirty_for_io(struct page if (mapping) { if (TestClearPageDirty(page)) { - if (mapping_cap_account_dirty(mapping)) + if (mapping_cap_account_dirty(mapping)) { + page_mkclean(page); dec_page_state(nr_dirty); + } return 1; } return 0; Index: linux-2.6/mm/rmap.c =================================================================== --- linux-2.6.orig/mm/rmap.c 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/mm/rmap.c 2006-06-08 13:59:37.000000000 +0200 @@ -472,6 +472,70 @@ int page_referenced(struct page *page, i return referenced; } +static int page_mkclean_one(struct page *page, struct vm_area_struct *vma) +{ + struct mm_struct *mm = vma->vm_mm; + unsigned long address; + pte_t *pte, entry; + spinlock_t *ptl; + int ret = 0; + + address = vma_address(page, vma); + if (address == -EFAULT) + goto out; + + pte = page_check_address(page, mm, address, &ptl); + if (!pte) + goto out; + + if (!pte_write(*pte)) + goto unlock; + + entry = ptep_get_and_clear(mm, address, pte); + entry = pte_mkclean(pte_wrprotect(entry)); + ptep_establish(vma, address, pte, entry); + lazy_mmu_prot_update(entry); + ret = 1; + +unlock: + pte_unmap_unlock(pte, ptl); +out: + return ret; +} + +static int page_mkclean_file(struct address_space *mapping, struct page *page) +{ + pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); + struct vm_area_struct *vma; + struct prio_tree_iter iter; + int ret = 0; + + BUG_ON(PageAnon(page)); + + spin_lock(&mapping->i_mmap_lock); + vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { + if (is_shared_writable(vma->vm_flags)) + ret += page_mkclean_one(page, vma); + } + spin_unlock(&mapping->i_mmap_lock); + return ret; +} + +int page_mkclean(struct page *page) +{ + int ret = 0; + + BUG_ON(!PageLocked(page)); + + if (page_mapped(page)) { + struct address_space *mapping = page_mapping(page); + if (mapping) + ret = page_mkclean_file(mapping, page); + } + + return ret; +} + /** * page_set_anon_rmap - setup new anonymous rmap * @page: the page to add the mapping to Index: linux-2.6/include/linux/rmap.h =================================================================== --- linux-2.6.orig/include/linux/rmap.h 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/include/linux/rmap.h 2006-06-08 13:59:37.000000000 +0200 @@ -105,6 +105,14 @@ pte_t *page_check_address(struct page *, */ unsigned long page_address_in_vma(struct page *, struct vm_area_struct *); +/* + * Cleans the PTEs of shared mappings. + * (and since clean PTEs should also be readonly, write protects them too) + * + * returns the number of cleaned PTEs. + */ +int page_mkclean(struct page *); + #else /* !CONFIG_MMU */ #define anon_vma_init() do {} while (0) Index: linux-2.6/fs/buffer.c =================================================================== --- linux-2.6.orig/fs/buffer.c 2006-06-08 13:59:35.000000000 +0200 +++ linux-2.6/fs/buffer.c 2006-06-08 13:59:37.000000000 +0200 @@ -2985,6 +2985,7 @@ int try_to_free_buffers(struct page *pag spin_lock(&mapping->private_lock); ret = drop_buffers(page, &buffers_to_free); + spin_unlock(&mapping->private_lock); if (ret) { /* * If the filesystem writes its buffers by hand (eg ext3) @@ -2996,7 +2997,6 @@ int try_to_free_buffers(struct page *pag */ clear_page_dirty(page); } - spin_unlock(&mapping->private_lock); out: if (buffers_to_free) { struct buffer_head *bh = buffers_to_free; Index: linux-2.6/drivers/char/drm/drm_vm.c =================================================================== --- linux-2.6.orig/drivers/char/drm/drm_vm.c 2006-04-07 10:54:38.000000000 +0200 +++ linux-2.6/drivers/char/drm/drm_vm.c 2006-06-08 14:11:37.000000000 +0200 @@ -574,7 +574,10 @@ int drm_mmap(struct file *filp, struct v #else /* Ye gads this is ugly. With more thought we could move this up higher and use - `protection_map' instead. */ + `protection_map' instead. + + One cannot; drivers are not allowed to 'reset' + vm_page_prot from vm_flags. */ vma->vm_page_prot = __pgprot(pte_val (pte_wrprotect
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