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authorChristoph Lameter <clameter@sgi.com>2006-05-01 15:16:08 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-05-01 21:17:45 -0400
commit4c28f81193b6778f7b49090930d88e6d12bcb928 (patch)
tree5e0d83368e7282060b8de5e73f13eb6003e99391 /mm
parenta4b741e380cb56045ccea36f2dbc10e42af21f24 (diff)
[PATCH] page migration: Fix fallback behavior for dirty pages
Currently we check PageDirty() in order to make the decision to swap out the page. However, the dirty information may be only be contained in the ptes pointing to the page. We need to first unmap the ptes before checking for PageDirty(). If unmap is successful then the page count of the page will also be decreased so that pageout() works properly. This is a fix necessary for 2.6.17. Without this fix we may migrate dirty pages for filesystems without migration functions. Filesystems may keep pointers to dirty pages. Migration of dirty pages can result in the filesystem keeping pointers to freed pages. Unmapping is currently not be separated out from removing all the references to a page and moving the mapping. Therefore try_to_unmap will be called again in migrate_page() if the writeout is successful. However, it wont do anything since the ptes are already removed. The coming updates to the page migration code will restructure the code so that this is no longer necessary. Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/migrate.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index d444229f2599..1c25040693d2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -439,6 +439,17 @@ redo:
439 goto unlock_both; 439 goto unlock_both;
440 } 440 }
441 441
442 /* Make sure the dirty bit is up to date */
443 if (try_to_unmap(page, 1) == SWAP_FAIL) {
444 rc = -EPERM;
445 goto unlock_both;
446 }
447
448 if (page_mapcount(page)) {
449 rc = -EAGAIN;
450 goto unlock_both;
451 }
452
442 /* 453 /*
443 * Default handling if a filesystem does not provide 454 * Default handling if a filesystem does not provide
444 * a migration function. We can only migrate clean 455 * a migration function. We can only migrate clean