On Wed, Apr 28, 2010 at 06:34:17PM +0100, Mel Gorman wrote: > Well, in the easiest case, the details of the VMA (particularly vm_start > and vm_pgoff) can confuse callers of vma_address during rmap_walk. In the > case of migration, it will return other false positives or negatives. false positives are fine ;). Only problems are false negatives... > > After you fix vma_adjust to be as safe as expand_downards you've also > > to take care of the rmap_walk that may run on a page->mapping = > > anon_vma that isn't the vma->anon_vma and you're not taking that > > anon_vma->lock of the shared page, when you change the vma > > vm_pgoff/vm_start. > > Is this not what the try-lock-different-vmas-or-backoff-and-retry logic > in patch 2 is doing or am I missing something else? yes exactly. This is why patch 2 can't be dropped, both for the vma_adjust and the rmap_walk that are really two separate issues. > How so? The old PTE should have been left in place, the page count of > the page remain positive and migration not occur. Right only problem is for remove_migration_ptes (and for both split_huge_page rmap_walks). For migrate the only issue is the second rmap_walk. > Because the list could be very large, it would make more sense to > introduce the shared lock if this is what was required. Kind of agree, we'll see... -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>