On Fri, Feb 27, 2015 at 01:48:48PM +0800, Wang, Yalin wrote: > > -----Original Message----- > > From: Minchan Kim [mailto:minchan.kim@xxxxxxxxx] On Behalf Of Minchan Kim > > Sent: Friday, February 27, 2015 1:28 PM > > To: Wang, Yalin > > Cc: Michal Hocko; Andrew Morton; linux-kernel@xxxxxxxxxxxxxxx; linux- > > mm@xxxxxxxxx; Rik van Riel; Johannes Weiner; Mel Gorman; Shaohua Li > > Subject: Re: [RFC] mm: change mm_advise_free to clear page dirty > > > > Hello, > > > > On Fri, Feb 27, 2015 at 11:37:18AM +0800, Wang, Yalin wrote: > > > This patch add ClearPageDirty() to clear AnonPage dirty flag, > > > the Anonpage mapcount must be 1, so that this page is only used by > > > the current process, not shared by other process like fork(). > > > if not clear page dirty for this anon page, the page will never be > > > treated as freeable. > > > > In case of anonymous page, it has PG_dirty when VM adds it to > > swap cache and clear it in clear_page_dirty_for_io. That's why > > I added ClearPageDirty if we found it in swapcache. > > What case am I missing? It would be better to understand if you > > describe specific scenario. > > > > Thanks. > > > > > > > > Signed-off-by: Yalin Wang <yalin.wang@xxxxxxxxxxxxxx> > > > --- > > > mm/madvise.c | 15 +++++---------- > > > 1 file changed, 5 insertions(+), 10 deletions(-) > > > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > > index 6d0fcb8..257925a 100644 > > > --- a/mm/madvise.c > > > +++ b/mm/madvise.c > > > @@ -297,22 +297,17 @@ static int madvise_free_pte_range(pmd_t *pmd, > > unsigned long addr, > > > continue; > > > > > > page = vm_normal_page(vma, addr, ptent); > > > - if (!page) > > > + if (!page || !PageAnon(page) || !trylock_page(page)) > > > continue; > > > > > > if (PageSwapCache(page)) { > > > - if (!trylock_page(page)) > > > + if (!try_to_free_swap(page)) > > > continue; > > > - > > > - if (!try_to_free_swap(page)) { > > > - unlock_page(page); > > > - continue; > > > - } > > > - > > > - ClearPageDirty(page); > > > - unlock_page(page); > > > } > > > > > > + if (page_mapcount(page) == 1) > > > + ClearPageDirty(page); > > > + unlock_page(page); > > > /* > > > * Some of architecture(ex, PPC) don't update TLB > > > * with set_pte_at and tlb_remove_tlb_entry so for > > > -- > Yes, for page which is in SwapCache, it is correct, > But for anon page which is not in SwapCache, it is always > PageDirty(), so we should also clear dirty bit to make it freeable, No. Every anon page starts from !PageDirty and it has PG_dirty only when it's addeded into swap cache. If vm_swap_full turns on, a page in swap cache could have PG_dirty via try_to_free_swap again. So, Do you have concern about swapped-out pages when MADV_FREE is called? If so, please look at my patch. https://lkml.org/lkml/2015/2/25/43 It will zap the swapped out page. So, this is not a issue any more? > > Another problem is that if an anon page is shared by more than one process, > This happened when fork(), the anon page will be copy on write, > In this case, we should not clear page dirty, > This is not correct for other process which don't call MADV_FREE syscall. You mean we shouldn't inherit MADV_FREE attribute? Why? parent: ptr1 = malloc(len); -> allocator calls mmap(len); memset(ptr1, 'a', len); free(ptr1); -> allocator calss madvise_free(ptr1, len); .. .. -> VM discard hinted pages fork(); child: ptr2 = malloc(len) -> allocator reuses the chunk allocated from parent. so, child will see zero pages from ptr2 but he doesn't write anything so garbage|zero page anything is okay to him. > > Thanks > > -- Kind regards, Minchan Kim -- 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>