On Mon, Oct 26, 2015 at 07:09:15PM -0700, Hugh Dickins 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. Thanks! > Kudos also to Hannes for suggesting this approach originally, I think. I should buy beer or soju if Hannes likes. > > 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 Actutally, I didn't think about that but once you mentioned it, I realized that would be better. Thanks for the suggestion. > 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. Yeb, I will rebase all series from the beginning based on recent mmtom so I will vanish the mess in git-blame. When I rebases it in mmotm, I will do it before reaching THP refcount new design if Andrew and Kirill don't mind it because it makes to fail my test as I reported. I don't know it's long time unknown bug or something THP-ref new introduces. Anyway, I want to test smoothly. > > 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 Thanks for testing! > 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? Right. > > 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. Exactly. -- 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>