>> >> >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:
Comments?
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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