On Mon, Oct 29, 2012 at 07:28:57PM +0100, Jan Kara wrote:
> On Fri 26-10-12 18:36:08, Darrick J. Wong wrote:
> > Create a helper function to decide if a particular address space is backed by a
> > device that requires stable page writes. For each wait_on_page_writeback call
> > that was inserted in the original stable page write patchset, change it to wait
> > only if the helper says it's necessary. This should eliminate unnecessary
> > waiting for devices that don't require page contents to be immutable during
> > writeout.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> >
> > fs/buffer.c | 3 ++-
> > fs/ext4/inode.c | 4 ++--
> > include/linux/fs.h | 2 ++
> > mm/filemap.c | 3 ++-
> > mm/page-writeback.c | 7 +++++++
> > 5 files changed, 15 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/buffer.c b/fs/buffer.c
> > index b5f0442..f508ece 100644
> > --- a/fs/buffer.c
> > +++ b/fs/buffer.c
> > @@ -2334,7 +2334,8 @@ int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> > if (unlikely(ret < 0))
> > goto out_unlock;
> > set_page_dirty(page);
> > - wait_on_page_writeback(page);
> > + if (page->mapping && mapping_needs_stable_writes(page->mapping))
> > + wait_on_page_writeback(page);
> The page is locked and we checked whether it belongs to the right mapping
> just after we locked it down. So you can safely skip the page->mapping
> test.
>
> > return 0;
> > out_unlock:
> > unlock_page(page);
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index b3c243b..82908b8 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -4813,8 +4813,8 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> > if (page_has_buffers(page)) {
> > if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
> > ext4_bh_unmapped)) {
> > - /* Wait so that we don't change page under IO */
> > - wait_on_page_writeback(page);
> > + if (mapping_needs_stable_writes(mapping))
> > + wait_on_page_writeback(page);
> > ret = VM_FAULT_LOCKED;
> > goto out;
> > }
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index b33cfc9..d99db0e 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -466,6 +466,8 @@ struct block_device {
> > struct percpu_rw_semaphore bd_block_size_semaphore;
> > };
> >
> > +int mapping_needs_stable_writes(struct address_space *mapping);
> > +
> > /*
> > * Radix-tree tags, for tagging dirty and writeback pages within the pagecache
> > * radix trees
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 83efee7..aedc6bd 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2274,7 +2274,8 @@ repeat:
> > return NULL;
> > }
> > found:
> > - wait_on_page_writeback(page);
> > + if (mapping_needs_stable_writes(mapping))
> > + wait_on_page_writeback(page);
> > return page;
> > }
> > EXPORT_SYMBOL(grab_cache_page_write_begin);
> > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > index 830893b..d0f042c 100644
> > --- a/mm/page-writeback.c
> > +++ b/mm/page-writeback.c
> > @@ -2275,3 +2275,10 @@ int mapping_tagged(struct address_space *mapping, int tag)
> > return radix_tree_tagged(&mapping->page_tree, tag);
> > }
> > EXPORT_SYMBOL(mapping_tagged);
> > +
> > +int mapping_needs_stable_writes(struct address_space *mapping)
> > +{
> > + return mapping->backing_dev_info &&
> > + bdi_cap_stable_writes(mapping->backing_dev_info);
> > +}
> > +EXPORT_SYMBOL_GPL(mapping_needs_stable_writes);
> Traditional name for these shortcuts is "mapping_cap_..." and put them in
> linux/backing-dev.h. And you don't have to check
> mapping->backing_dev_info.
Ok, I've removed both of those checks. Thank you for the comments!
--D
>
> Honza
> --
> Jan Kara <jack@xxxxxxx>
> SUSE Labs, CR
> --
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