On Sat, Feb 28, 2015 at 10:11:13AM +0800, Wang, Yalin wrote: > > -----Original Message----- > > From: Michal Hocko [mailto:mstsxfx@xxxxxxxxx] On Behalf Of Michal Hocko > > Sent: Saturday, February 28, 2015 5:03 AM > > To: Wang, Yalin > > Cc: 'Minchan Kim'; 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 > > > > On Fri 27-02-15 11:37:18, 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. > > > > Very well spotted! I haven't noticed that during the review. > > > > > 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; > > > > PageAnon check seems to be redundant because we are not allowing > > MADV_FREE on any !anon private mappings AFAIR. > I only see this check: > /* MADV_FREE works for only anon vma at the moment */ > if (vma->vm_file) > return -EINVAL; > > but for file private map, there are also AnonPage sometimes, do we need change > to like this: > if (vma->vm_flags & VM_SHARED) > return -EINVAL; I couldn't understand your point. In this stage, we intentionally disabled madvise_free on file mapped area(AFAIRC, some guys tried it long time ago but it had many issues so dropped). So, how can file-private mmaped can reach this code? Could you elaborate it more about that why we need PageAnon check in here? > > > > > > if (PageSwapCache(page)) { > > > - if (!trylock_page(page)) > > > + if (!try_to_free_swap(page)) > > > continue; > > > > You need to unlock the page here. > Good spot. > > > > - > > > - if (!try_to_free_swap(page)) { > > > - unlock_page(page); > > > - continue; > > > - } > > > - > > > - ClearPageDirty(page); > > > - unlock_page(page); > > > } > > > > > > + if (page_mapcount(page) == 1) > > > + ClearPageDirty(page); > > > > Please add a comment about why we need to ClearPageDirty even > > !PageSwapCache. Anon pages are usually not marked dirty AFAIR. The > > reason seem to be racing try_to_free_swap which sets the page that way > > (although I do not seem to remember why are we doing that in the first > > place...) > > > Use page_mapcount to judge if a page can be clear dirty flag seems > Not a very good solution, that is because we don't know how many > ptes are share this page, I am thinking if there is some good solution > For shared AnonPage. > -- 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>