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.
>
> if (PageSwapCache(page)) {
> - if (!trylock_page(page))
> + if (!try_to_free_swap(page))
> continue;
You need to unlock the page here.
> -
> - 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...)
> + unlock_page(page);
> /*
> * Some of architecture(ex, PPC) don't update TLB
> * with set_pte_at and tlb_remove_tlb_entry so for
> --
> 2.2.2
--
Michal Hocko
SUSE Labs
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