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Message-ID: <4df4ef0c0801170416s5581ae28h90d91578baa77738@mail.gmail.com>
Date: Thu, 17 Jan 2008 15:16:55 +0300
From: "Anton Salikhmetov" <salikhmetov@...il.com>
To: "Miklos Szeredi" <miklos@...redi.hu>
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, r.e.wolff@...wizard.nl,
hidave.darkstar@...il.com, hch@...radead.org
Subject: Re: [PATCH -v5 2/2] Updating ctime and mtime at syncing
2008/1/17, Miklos Szeredi <miklos@...redi.hu>:
> > 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.
I've already described this change in one of my previous emails:
> 4. Recording the time was the file data changed
>
> Finally, I noticed yet another issue with the previous version of my patch.
> Specifically, the time stamps were set to the current time of the moment
> when syncing but not the write reference was being done. This led to the
> following adverse effect on my development system:
>
> 1) a text file A was updated by process B;
> 2) process B exits without calling any of the *sync() functions;
> 3) vi editor opens the file A;
> 4) file data synced, file times updated;
> 5) vi is confused by "thinking" that the file was changed after 3).
>
> This version overcomes this problem by introducing another field into the
> address_space structure. This field is used to "remember" the time of
> dirtying, and then this time value is propagated to the file metadata.
>
> This approach is based upon the following suggestion given by Peter
> Staubach during one of our previous discussions:
>
> http://lkml.org/lkml/2008/1/9/267
>
> > A better architecture would be to arrange for the file times
> > to be updated when the page makes the transition from being
> > unmodified to modified. This is not straightforward due to
> > the current locking, but should be doable, I think. Perhaps
> > recording the current time and then using it to update the
> > file times at a more suitable time (no pun intended) might
> > work.
>
> The solution I propose now proves the viability of the latter
> approach.
See:
http://lkml.org/lkml/2008/1/15/202
>
> > + 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.
Thanks for your suggestion, I'll consider how I can apply it.
>
> > +
> > 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().
Thanks for your suggestion, I'll consider how I can apply it.
However, I suspect that this is a bit problematic. Let me check it out.
>
> > 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.
The first part is necessary to account for "remembering" the modification time.
The second part is for handling block device files. I cannot see any other
sane way to update file times for them.
>
> >
> > 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.
This change is a logical consequence of introducing
the new inode_update_time() routine, which was explained above.
>
> >
> > 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.
I haven't found any locks with bigger granularity here. Frankly, I do
not think that this should be a big performance hit if we acquire and
release the lock for each PTE. However, I'll be grateful for any further
suggestions.
Rik, can you please comment on this?
>
> > +/*
> > * 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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