On Tue, 17 Apr 2012 13:29:25 +0100 Mel Gorman <mgorman@xxxxxxx> wrote: > On Mon, Apr 16, 2012 at 05:50:40PM +0200, Martin Schwidefsky wrote: > > On Mon, 16 Apr 2012 15:14:23 +0100 > > Mel Gorman <mgorman@xxxxxxx> wrote: > > > > > This patch is horribly ugly and there has to be a better way of doing > > > it. I'm looking for suggestions on what s390 can do here that is not > > > painful or broken. > > > > > > However, s390 needs a better way of guarding against > > > PageSwapCache pages being removed from the radix tree while set_page_dirty() > > > is being called. The patch would be marginally better if in the PageSwapCache > > > case we simply tried to lock once and in the contended case just fail to > > > propogate the storage key. I lack familiarity with the s390 architecture > > > to be certain if this is safe or not. Suggestions on a better fix? > > > > One though that crossed my mind is that maybe a better approach would be > > to move the page_test_and_clear_dirty check out of page_remove_rmap. > > What we need to look out for are code sequences of the form: > > > > if (pte_dirty(pte)) > > set_page_dirty(page); > > ... > > page_remove_rmap(page); > > > > There are four of those as far as I can see: in try_to_unmap_one, > > try_to_unmap_cluster, zap_pte, and zap_pte_range. > > > > A valid implementation for s390 would be to test and clear the changed > > bit in the storage key for every of those pte_dirty() calls. > > > > if (pte_dirty(pte) || page_test_and_clear_dirty(page)) > > set_page_dirty(page); > > ... > > page_remove_rmap(page); /* w/o page_test_clear_dirty */ > > > > In the zap_pte_range() case at least, pte_dirty() is only being checked > for !PageAnon pages so if we took this approach we would miss > PageSwapCache pages. If we added the check then the same problem is hit > and we'd need additional logic there for s390 to drop the PTL, take the > page lock and retry the operation. It'd still be ugly :( Well if x86 can get away with ignoring PageSwapCache pages in zap_pte_range() pages then s390 should be able to get away with it as well, no ? -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>