On Mon, 2008-08-11 at 15:25 +0900, Hisashi Hifumi wrote:
> >> >> >I am wondering why we need stronger invalidate hurantees for DIO->
> >> >> >invalidate_inode_pages_range(),which force the page being removed from
> >> >> >page cache? In case of bh is busy due to ext3 writeout,
> >> >> >journal_try_to_free_buffers() could return different error number(EBUSY)
> >> >> >to try_to_releasepage() (instead of EIO). In that case, could we just
> >> >> >leave the page in the cache, clean pageuptodate() (to force later buffer
> >> >> >read to read from disk) and then invalidate_complete_page2() return
> >> >> >successfully? Any issue with this way?
> >> >>
> >> >> My idea is that journal_try_to_free_buffers returns EBUSY if it fails due to
> >> >> bh busy, and dio write falls back to buffered write. This is easy to fix.
> >> >>
> >> >>
> >> >
> >> >What about the invalidates done after the DIO has already run
> >> >non-buffered?
> >>
> >> Dio write falls back to buffered IO when writing to a hole on ext3, I
> >think. I want to
> >> apply this mechanism to fix this issue. When try_to_release_page fails on
> >a page
> >> due to bh busy, dio write does buffered write, sync_page_range, and
> >> wait_on_page_writeback, imvalidates page cache to preserve dio semantics.
> >> Even if page invalidation that is carried out after
> >wait_on_page_writeback fails,
> >> there is no inconsistency between HDD and page cache.
> >>
> >
> >Sorry, I'm sure I wasn't very clear, I was referencing this code from
> >mm/filemap.c:
> >
> > written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
> >
> > /*
> > * Finally, try again to invalidate clean pages which might have been
> > * cached by non-direct readahead, or faulted in by get_user_pages()
> > * if the source of the write was an mmap'ed region of the file
> > * we're writing. Either one is a pretty crazy thing to do,
> > * so we don't support it 100%. If this invalidation
> > * fails, tough, the write still worked...
> > */
> > if (mapping->nrpages) {
> > invalidate_inode_pages2_range(mapping,
> > pos >> PAGE_CACHE_SHIFT, end);
> > }
> >
> >If this second invalidate fails during a DIO write, we'll have up to
> >date pages in cache that don't match the data on disk. It is unlikely
> >to fail because the conditions that make jbd unable to free a buffer are
> >rare, but it can still happen with the write combination of mmap usage.
> >
> >The good news is the second invalidate doesn't make O_DIRECT return
> >-EIO. But, it sounds like fixing do_launder_page to always call into
> >the FS can fix all of these problems. Am I missing something?
> >
>
> My approach is not implementing do_launder_page for ext3.
> It is needed to modify VFS.
>
> My patch is as follows:
Sorry, I'm still not sure why the do_launder_page implementation is a
bad idea. Clearly Mingming spent quite some time on it in the past, but
given that it could provide a hook for the FS to do expensive operations
to make the page really go away, why not do it?
As far as I can tell, the only current users afs, nfs and fuse. Pushing
down the PageDirty check to those filesystems should be trivial.
With that said, I don't have strong feelings against falling back to
buffered IO when the invalidate fails. Maybe Zach remembers something I
don't?
-chris
>
>
> diff -Nrup linux-2.6.27-rc2.org/mm/filemap.c linux-2.6.27-rc2/mm/filemap.c
> --- linux-2.6.27-rc2.org/mm/filemap.c 2008-08-11 14:33:23.000000000 +0900
> +++ linux-2.6.27-rc2/mm/filemap.c 2008-08-11 14:57:29.000000000 +0900
> @@ -2129,13 +2129,16 @@ generic_file_direct_write(struct kiocb *
> * After a write we want buffered reads to be sure to go to disk to get
> * the new data. We invalidate clean cached page from the region we're
> * about to write. We do this *before* the write so that we can return
> - * -EIO without clobbering -EIOCBQUEUED from ->direct_IO().
> + * -EBUSY without clobbering -EIOCBQUEUED from ->direct_IO().
> */
> if (mapping->nrpages) {
> written = invalidate_inode_pages2_range(mapping,
> pos >> PAGE_CACHE_SHIFT, end);
> - if (written)
> + if (written) {
> + if (written == -EBUSY)
> + written = 0;
> goto out;
> + }
> }
>
> written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
> diff -Nrup linux-2.6.27-rc2.org/mm/truncate.c linux-2.6.27-rc2/mm/truncate.c
> --- linux-2.6.27-rc2.org/mm/truncate.c 2008-08-11 14:33:24.000000000 +0900
> +++ linux-2.6.27-rc2/mm/truncate.c 2008-08-11 14:52:03.000000000 +0900
> @@ -380,7 +380,7 @@ static int do_launder_page(struct addres
> * Any pages which are found to be mapped into pagetables are unmapped prior to
> * invalidation.
> *
> - * Returns -EIO if any pages could not be invalidated.
> + * Returns -EBUSY if any pages could not be invalidated.
> */
> int invalidate_inode_pages2_range(struct address_space *mapping,
> pgoff_t start, pgoff_t end)
> @@ -440,7 +440,7 @@ int invalidate_inode_pages2_range(struct
> ret2 = do_launder_page(mapping, page);
> if (ret2 == 0) {
> if (!invalidate_complete_page2(mapping, page))
> - ret2 = -EIO;
> + ret2 = -EBUSY;
> }
> if (ret2 < 0)
> ret = ret2;
>
>
>
>
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