Hello Yalin, Sorry for missing you in Cc list. IIRC, mails to send your previous mail address(Yalin.Wang@xxxxxxxxxxxxxx) were returned. On Tue, Oct 27, 2015 at 11:44:09AM +0800, yalin wang wrote: > > > On Oct 27, 2015, at 10:09, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > > > On Mon, 19 Oct 2015, Minchan Kim wrote: > > > >> I made reclaim path mess to check and free MADV_FREEed page. > >> This patch simplify it with tweaking add_to_swap. > >> > >> So far, we mark page as PG_dirty when we add the page into > >> swap cache(ie, add_to_swap) to page out to swap device but > >> this patch moves PG_dirty marking under try_to_unmap_one > >> when we decide to change pte from anon to swapent so if > >> any process's pte has swapent for the page, the page must > >> be swapped out. IOW, there should be no funcional behavior > >> change. It makes relcaim path really simple for MADV_FREE > >> because we just need to check PG_dirty of page to decide > >> discarding the page or not. > >> > >> Other thing this patch does is to pass TTU_BATCH_FLUSH to > >> try_to_unmap when we handle freeable page because I don't > >> see any reason to prevent it. > >> > >> Cc: Hugh Dickins <hughd@xxxxxxxxxx> > >> Cc: Mel Gorman <mgorman@xxxxxxx> > >> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > > > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> > > > > This is sooooooo much nicer than the code it replaces! Really good. > > Kudos also to Hannes for suggesting this approach originally, I think. > > > > I hope this implementation satisfies a good proportion of the people > > who have been wanting MADV_FREE: I'm not among them, and have long > > lost touch with those discussions, so won't judge how usable it is. > > > > I assume you'll refactor the series again before it goes to Linus, > > so the previous messier implementations vanish? I notice Andrew > > has this "mm: simplify reclaim path for MADV_FREE" in mmotm as > > mm-dont-split-thp-page-when-syscall-is-called-fix-6.patch: > > I guess it all got much too messy to divide up in a hurry. > > > > I've noticed no problems in testing (unlike the first time you moved > > to working with pte_dirty); though of course I've not been using > > MADV_FREE itself at all. > > > > One aspect has worried me for a while, but I think I've reached the > > conclusion that it doesn't matter at all. The swap that's allocated > > in add_to_swap() would normally get freed again (after try_to_unmap > > found it was a MADV_FREE !pte_dirty !PageDirty case) at the bottom > > of shrink_page_list(), in __remove_mapping(), yes? > > > > The bit that worried me is that on rare occasions, something unknown > > might take a speculative reference to the page, and __remove_mapping() > > fail to freeze refs for that reason. Much too rare to worry over not > > freeing that page immediately, but it leaves us with a PageUptodate > > PageSwapCache !PageDirty page, yet its contents are not the contents > > of that location on swap. > > > > But since this can only happen when you have *not* inserted the > > corresponding swapent anywhere, I cannot think of anything that would > > have a legitimate interest in its contents matching that location on swap. > > So I don't think it's worth looking for somewhere to add a SetPageDirty > > (or a delete_from_swap_cache) just to regularize that case. > > > >> --- > >> include/linux/rmap.h | 6 +---- > >> mm/huge_memory.c | 5 ---- > >> mm/rmap.c | 42 ++++++---------------------------- > >> mm/swap_state.c | 5 ++-- > >> mm/vmscan.c | 64 ++++++++++++++++------------------------------------ > >> 5 files changed, 30 insertions(+), 92 deletions(-) > >> <snip> You added comment bottom line so I'm not sure what PageDirty you meant. > it is wrong here if you only check PageDirty() to decide if the page is freezable or not . > The Anon page are shared by multiple process, _mapcount > 1 , > so you must check all pt_dirty bit during page_referenced() function, > see this mail thread: > http://ns1.ske-art.com/lists/kernel/msg1934021.html If one of pte among process sharing the page was dirty, the dirtiness should be propagated from pte to PG_dirty by try_to_unmap_one. IOW, if the page doesn't have PG_dirty flag, it means all of process did MADV_FREE. Am I missing something from you question? If so, could you show exact scenario I am missing? Thanks for the interest. > Thanks > > > > > > > > > -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>