Messages in this thread Patches in this message | | | Date | Sun, 21 Oct 2007 23:19:41 +0300 | From | Artem Bityutskiy <> | Subject | forcing write-back from FS - again |
| |
Hi Andrew,
some time ago we were talking about doing write-back from inside a file-system (http://marc.info/?l=linux-kernel&m=119097117713616&w=2). You said that I'm not the only person who needs this, because the same thing is needed for delayed allocation.
The problem is that if we initiate write-back from prepare_write() and we are having a dirty page lock, we deadlock in write_cache_pages() which tries to lock the same page.
You suggested to enhance struct writeback_control and put page that should be skipped.
I tried something like
diff --git a/include/linux/writeback.h b/include/linux/writeback.h --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -61,6 +61,7 @@ struct writeback_control { unsigned for_reclaim:1; /* Invoked from the page allocator */ unsigned for_writepages:1; /* This is a writepages() call */ unsigned range_cyclic:1; /* range_start is cyclic */ + struct page *skip_pg; /* do not write this page back */
void *fs_private; /* For use by ->writepages() */ }; diff --git a/mm/page-writeback.c b/mm/page-writeback.c --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -641,6 +641,9 @@ retry: for (i = 0; i < nr_pages; i++) { struct page *page = pvec.pages[i];
+ if (unlikely(page == wbc->skip_pg)) + continue; + /* * At this point we hold neither mapping->tree_lock nor * lock on the page itself: the page may be truncated but it does not dot actually work, because if we have two processes forcing write-back from write_page(), they will mutually deadlock (A waits in write_cache_pages() on a page B has locked, B waits on inode or page A has locked).
So this way is not ok, do you have any other ideas?
We could mark page clean temporarily before doing write-back, and mark it dirty again, but this seems to be inefficient (although I'm not sure, need to dig these functions deeper, but they _seem_ to traverse the radix tree and change tags, so marking one page dirty may need to change many tags, but again, I did not really dig tis yet).
I'd appreciate any suggestions. Thanks!
-- Best Regards, Artem Bityutskiy (Артём Битюцкий) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |