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Message-Id: <E1JFSgG-0006G1-6V@pomaz-ex.szeredi.hu>
Date: Thu, 17 Jan 2008 12:13:08 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: salikhmetov@...il.com
CC: linux-mm@...ck.org, jakob@...hought.net,
linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
riel@...hat.com, ksm@...dk, staubach@...hat.com,
jesper.juhl@...il.com, torvalds@...ux-foundation.org,
a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
protasnb@...il.com, miklos@...redi.hu, r.e.wolff@...wizard.nl,
hidave.darkstar@...il.com, hch@...radead.org
Subject: Re: [PATCH -v5 2/2] Updating ctime and mtime at syncing
> http://bugzilla.kernel.org/show_bug.cgi?id=2645
>
> Changes for updating the ctime and mtime fields for memory-mapped files:
>
> 1) a new flag triggering update of the inode data;
> 2) a new field in the address_space structure for saving modification time;
> 3) a new helper function to update ctime and mtime when needed;
> 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> 5) implementing lazy ctime and mtime update.
OK, the functionality seems to be there now. As a next step, I think
you should try to simplify the patch, removing everything, that is not
strictly necessary.
>
> Signed-off-by: Anton Salikhmetov <salikhmetov@...il.com>
> ---
> fs/buffer.c | 3 ++
> fs/fs-writeback.c | 2 +
> fs/inode.c | 43 +++++++++++++++++++++++----------
> fs/sync.c | 2 +
> include/linux/fs.h | 13 +++++++++-
> include/linux/pagemap.h | 3 +-
> mm/msync.c | 61 +++++++++++++++++++++++++++++++++-------------
> mm/page-writeback.c | 54 ++++++++++++++++++++++-------------------
> 8 files changed, 124 insertions(+), 57 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 7249e01..3967aa7 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -701,6 +701,9 @@ static int __set_page_dirty(struct page *page,
> if (unlikely(!mapping))
> return !TestSetPageDirty(page);
>
> + mapping->mtime = CURRENT_TIME;
Why is this needed? POSIX explicitly states, that the modification
time can be set to anywhere between the first write and the msync.
> + set_bit(AS_MCTIME, &mapping->flags);
A bigger problem is that doing this in __set_page_dirty() and friends
will mean, that the flag will be set for non-mapped writes as well,
which we definitely don't want.
A better place to put it is do_wp_page and __do_fault, where
set_page_dirty_balance() is called.
> +
> if (TestSetPageDirty(page))
> return 0;
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 300324b..affd291 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -243,6 +243,8 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
>
> spin_unlock(&inode_lock);
>
> + mapping_update_time(mapping);
> +
I think this is unnecessary. Rather put the update into remove_vma().
> ret = do_writepages(mapping, wbc);
>
> /* Don't write the inode if only I_DIRTY_PAGES was set */
> diff --git a/fs/inode.c b/fs/inode.c
> index ed35383..edd5bf4 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1243,8 +1243,10 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
> EXPORT_SYMBOL(touch_atime);
>
> /**
> - * file_update_time - update mtime and ctime time
> - * @file: file accessed
> + * inode_update_time - update mtime and ctime time
> + * @inode: inode accessed
> + * @ts: time when inode was accessed
> + * @sync: whether to do synchronous update
> *
> * Update the mtime and ctime members of an inode and mark the inode
> * for writeback. Note that this function is meant exclusively for
> @@ -1253,11 +1255,8 @@ EXPORT_SYMBOL(touch_atime);
> * S_NOCTIME inode flag, e.g. for network filesystem where these
> * timestamps are handled by the server.
> */
> -
> -void file_update_time(struct file *file)
> +void inode_update_time(struct inode *inode, struct timespec *ts)
> {
> - struct inode *inode = file->f_path.dentry->d_inode;
> - struct timespec now;
> int sync_it = 0;
>
> if (IS_NOCMTIME(inode))
> @@ -1265,22 +1264,41 @@ void file_update_time(struct file *file)
> if (IS_RDONLY(inode))
> return;
>
> - now = current_fs_time(inode->i_sb);
> - if (!timespec_equal(&inode->i_mtime, &now)) {
> - inode->i_mtime = now;
> + if (timespec_compare(&inode->i_mtime, ts) < 0) {
> + inode->i_mtime = *ts;
> sync_it = 1;
> }
>
> - if (!timespec_equal(&inode->i_ctime, &now)) {
> - inode->i_ctime = now;
> + if (timespec_compare(&inode->i_ctime, ts) < 0) {
> + inode->i_ctime = *ts;
> sync_it = 1;
> }
>
> if (sync_it)
> mark_inode_dirty_sync(inode);
> }
> +EXPORT_SYMBOL(inode_update_time);
>
> -EXPORT_SYMBOL(file_update_time);
> +/*
> + * Update the ctime and mtime stamps after checking if they are to be updated.
> + */
> +void mapping_update_time(struct address_space *mapping)
> +{
> + if (test_and_clear_bit(AS_MCTIME, &mapping->flags)) {
> + struct inode *inode = mapping->host;
> + struct timespec *ts = &mapping->mtime;
> +
> + if (S_ISBLK(inode->i_mode)) {
> + struct block_device *bdev = inode->i_bdev;
> +
> + mutex_lock(&bdev->bd_mutex);
> + list_for_each_entry(inode, &bdev->bd_inodes, i_devices)
> + inode_update_time(inode, ts);
> + mutex_unlock(&bdev->bd_mutex);
> + } else
> + inode_update_time(inode, ts);
> + }
> +}
All these changes to inode.c are unnecessary, I think.
>
> int inode_needs_sync(struct inode *inode)
> {
> @@ -1290,7 +1308,6 @@ int inode_needs_sync(struct inode *inode)
> return 1;
> return 0;
> }
> -
> EXPORT_SYMBOL(inode_needs_sync);
>
> int inode_wait(void *word)
> diff --git a/fs/sync.c b/fs/sync.c
> index 7cd005e..5561464 100644
> --- a/fs/sync.c
> +++ b/fs/sync.c
> @@ -87,6 +87,8 @@ long do_fsync(struct file *file, int datasync)
> goto out;
> }
>
> + mapping_update_time(mapping);
> +
> ret = filemap_fdatawrite(mapping);
>
> /*
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b3ec4a4..f0d3ced 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -511,6 +511,7 @@ struct address_space {
> spinlock_t private_lock; /* for use by the address_space */
> struct list_head private_list; /* ditto */
> struct address_space *assoc_mapping; /* ditto */
> + struct timespec mtime; /* modification time */
> } __attribute__((aligned(sizeof(long))));
> /*
> * On most architectures that alignment is already the case; but
> @@ -1977,7 +1978,17 @@ extern int buffer_migrate_page(struct address_space *,
> extern int inode_change_ok(struct inode *, struct iattr *);
> extern int __must_check inode_setattr(struct inode *, struct iattr *);
>
> -extern void file_update_time(struct file *file);
> +extern void inode_update_time(struct inode *, struct timespec *);
> +
> +static inline void file_update_time(struct file *file)
> +{
> + struct inode *inode = file->f_dentry->d_inode;
> + struct timespec ts = current_fs_time(inode->i_sb);
> +
> + inode_update_time(inode, &ts);
> +}
> +
> +extern void mapping_update_time(struct address_space *);
As is this.
>
> static inline ino_t parent_ino(struct dentry *dentry)
> {
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index db8a410..bf0f9e7 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -17,8 +17,9 @@
> * Bits in mapping->flags. The lower __GFP_BITS_SHIFT bits are the page
> * allocation mode flags.
> */
> -#define AS_EIO (__GFP_BITS_SHIFT + 0) /* IO error on async write */
> +#define AS_EIO (__GFP_BITS_SHIFT + 0) /* IO error on async write */
> #define AS_ENOSPC (__GFP_BITS_SHIFT + 1) /* ENOSPC on async write */
> +#define AS_MCTIME (__GFP_BITS_SHIFT + 2) /* mtime and ctime to update */
>
> static inline void mapping_set_error(struct address_space *mapping, int error)
> {
> diff --git a/mm/msync.c b/mm/msync.c
> index 44997bf..7657776 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -13,16 +13,37 @@
> #include <linux/syscalls.h>
>
> /*
> + * Scan the PTEs for pages belonging to the VMA and mark them read-only.
> + * It will force a pagefault on the next write access.
> + */
> +static void vma_wrprotect(struct vm_area_struct *vma)
> +{
> + unsigned long addr;
> +
> + for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {
> + spinlock_t *ptl;
> + pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
> + pud_t *pud = pud_offset(pgd, addr);
> + pmd_t *pmd = pmd_offset(pud, addr);
> + pte_t *pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> +
> + if (pte_dirty(*pte) && pte_write(*pte))
> + *pte = pte_wrprotect(*pte);
> + pte_unmap_unlock(pte, ptl);
> + }
> +}
> +
There might be a more efficient way to do this, than getting and
releasing the lock for each pte.
> +/*
> * MS_SYNC syncs the entire file - including mappings.
> *
> - * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
> - * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
> - * Now it doesn't do anything, since dirty pages are properly tracked.
> + * MS_ASYNC does not start I/O. Instead, it marks the relevant pages
> + * read-only by calling vma_wrprotect(). This is needed to catch the next
> + * write reference to the mapped region and update the file times
> + * accordingly.
> *
> - * The application may now run fsync() to
> - * write out the dirty pages and wait on the writeout and check the result.
> - * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
> - * async writeout immediately.
> + * The application may now run fsync() to write out the dirty pages and
> + * wait on the writeout and check the result. Or the application may run
> + * fadvise(FADV_DONTNEED) against the fd to start async writeout immediately.
> * So by _not_ starting I/O in MS_ASYNC we provide complete flexibility to
> * applications.
> */
> @@ -80,16 +101,22 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
> start = vma->vm_end;
>
> file = vma->vm_file;
> - if (file && (vma->vm_flags & VM_SHARED) && (flags & MS_SYNC)) {
> - get_file(file);
> - up_read(&mm->mmap_sem);
> - error = do_fsync(file, 0);
> - fput(file);
> - if (error)
> - goto out;
> - down_read(&mm->mmap_sem);
> - vma = find_vma(mm, start);
> - continue;
> + if (file && (vma->vm_flags & VM_SHARED)) {
> + if (flags & MS_ASYNC) {
> + vma_wrprotect(vma);
> + mapping_update_time(file->f_mapping);
> + }
> + if (flags & MS_SYNC) {
> + get_file(file);
> + up_read(&mm->mmap_sem);
> + error = do_fsync(file, 0);
> + fput(file);
> + if (error)
> + goto out;
> + down_read(&mm->mmap_sem);
> + vma = find_vma(mm, start);
> + continue;
> + }
> }
>
> vma = vma->vm_next;
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 3d3848f..53d0e34 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -997,35 +997,39 @@ int __set_page_dirty_no_writeback(struct page *page)
> */
> int __set_page_dirty_nobuffers(struct page *page)
> {
> - if (!TestSetPageDirty(page)) {
> - struct address_space *mapping = page_mapping(page);
> - struct address_space *mapping2;
> + struct address_space *mapping = page_mapping(page);
> + struct address_space *mapping2;
>
> - if (!mapping)
> - return 1;
> + if (!mapping)
> + return 1;
>
> - write_lock_irq(&mapping->tree_lock);
> - mapping2 = page_mapping(page);
> - if (mapping2) { /* Race with truncate? */
> - BUG_ON(mapping2 != mapping);
> - WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
> - if (mapping_cap_account_dirty(mapping)) {
> - __inc_zone_page_state(page, NR_FILE_DIRTY);
> - __inc_bdi_stat(mapping->backing_dev_info,
> - BDI_RECLAIMABLE);
> - task_io_account_write(PAGE_CACHE_SIZE);
> - }
> - radix_tree_tag_set(&mapping->page_tree,
> - page_index(page), PAGECACHE_TAG_DIRTY);
> - }
> - write_unlock_irq(&mapping->tree_lock);
> - if (mapping->host) {
> - /* !PageAnon && !swapper_space */
> - __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> + mapping->mtime = CURRENT_TIME;
> + set_bit(AS_MCTIME, &mapping->flags);
> +
> + if (TestSetPageDirty(page))
> + return 0;
> +
> + write_lock_irq(&mapping->tree_lock);
> + mapping2 = page_mapping(page);
> + if (mapping2) {
> + /* Race with truncate? */
> + BUG_ON(mapping2 != mapping);
> + WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
> + if (mapping_cap_account_dirty(mapping)) {
> + __inc_zone_page_state(page, NR_FILE_DIRTY);
> + __inc_bdi_stat(mapping->backing_dev_info,
> + BDI_RECLAIMABLE);
> + task_io_account_write(PAGE_CACHE_SIZE);
> }
> - return 1;
> + radix_tree_tag_set(&mapping->page_tree,
> + page_index(page), PAGECACHE_TAG_DIRTY);
> }
> - return 0;
> + write_unlock_irq(&mapping->tree_lock);
> +
> + if (mapping->host)
> + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +
> + return 1;
> }
> EXPORT_SYMBOL(__set_page_dirty_nobuffers);
>
> --
> 1.4.4.4
>
>
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