* Stephen Clark <[email protected]> [2006-12-29 10:17]:
> >It works for me now, both your testcase as well as an installation of
> >Debian on this ARM device. I manually applied the patch to 2.6.19.
>
> Can you post a diff against 2.6.19?
--- a/mm/page-writeback.c 2006-11-29 21:57:37.000000000 +0000
+++ b/mm/page-writeback.c 2006-12-29 11:02:55.555147896 +0000
@@ -893,16 +893,45 @@
{
struct address_space *mapping = page_mapping(page);
- if (mapping) {
+ if (mapping && mapping_cap_account_dirty(mapping)) {
+ /*
+ * Yes, Virginia, this is indeed insane.
+ *
+ * We use this sequence to make sure that
+ * (a) we account for dirty stats properly
+ * (b) we tell the low-level filesystem to
+ * mark the whole page dirty if it was
+ * dirty in a pagetable. Only to then
+ * (c) clean the page again and return 1 to
+ * cause the writeback.
+ *
+ * This way we avoid all nasty races with the
+ * dirty bit in multiple places and clearing
+ * them concurrently from different threads.
+ *
+ * Note! Normally the "set_page_dirty(page)"
+ * has no effect on the actual dirty bit - since
+ * that will already usually be set. But we
+ * need the side effects, and it can help us
+ * avoid races.
+ *
+ * We basically use the page "master dirty bit"
+ * as a serialization point for all the different
+ * threds doing their things.
+ *
+ * FIXME! We still have a race here: if somebody
+ * adds the page back to the page tables in
+ * between the "page_mkclean()" and the "TestClearPageDirty()",
+ * we might have it mapped without the dirty bit set.
+ */
+ if (page_mkclean(page))
+ set_page_dirty(page);
if (TestClearPageDirty(page)) {
- if (mapping_cap_account_dirty(mapping)) {
- page_mkclean(page);
- dec_zone_page_state(page, NR_FILE_DIRTY);
- }
+ dec_zone_page_state(page, NR_FILE_DIRTY);
return 1;
}
return 0;
- }
+ }
return TestClearPageDirty(page);
}
EXPORT_SYMBOL(clear_page_dirty_for_io);
--
Martin Michlmayr
http://www.cyrius.com/
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