| Message ID | 20220304093409.25829-16-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | A few cleanup and fixup patches for migration | expand |
Miaohe Lin <linmiaohe@huawei.com> writes: > When follow_page peeks a page, the page could be reclaimed under heavy > memory pressure I don't think that memory pressure and reclaiming will be an issue. > and thus be offlined while it's still being used by the > do_pages_stat_array(). "offline" seems a possible problem. Best Regards, Huang, Ying > Use FOLL_GET to hold the page refcnt to fix this > potential issue. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/migrate.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 7b1c0b988234..98a968e6f465 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1788,13 +1788,18 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > goto set_status; > > /* FOLL_DUMP to ignore special (like zero) pages */ > - page = follow_page(vma, addr, FOLL_DUMP); > + page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); > > err = PTR_ERR(page); > if (IS_ERR(page)) > goto set_status; > > - err = page ? page_to_nid(page) : -ENOENT; > + if (page) { > + err = page_to_nid(page); > + put_page(page); > + } else { > + err = -ENOENT; > + } > set_status: > *status = err;
On Mon, Mar 7, 2022 at 1:22 PM Huang, Ying <ying.huang@intel.com> wrote: > > Miaohe Lin <linmiaohe@huawei.com> writes: > > > When follow_page peeks a page, the page could be reclaimed under heavy > > memory pressure > > I don't think that memory pressure and reclaiming will be an issue. I think he means a page first to be reclaimed then to be offline could encounter this issue and reclaiming is a precondition. Thanks. > > > and thus be offlined while it's still being used by the > > do_pages_stat_array(). > > "offline" seems a possible problem.
Muchun Song <songmuchun@bytedance.com> writes: > On Mon, Mar 7, 2022 at 1:22 PM Huang, Ying <ying.huang@intel.com> wrote: >> >> Miaohe Lin <linmiaohe@huawei.com> writes: >> >> > When follow_page peeks a page, the page could be reclaimed under heavy >> > memory pressure >> >> I don't think that memory pressure and reclaiming will be an issue. > > I think he means a page first to be reclaimed then to be offline > could encounter this issue and reclaiming is a precondition. I don't think reclaiming is a precondition. It seems possible that the virtual page is migrated, then the physical page is offlined. Best Regards, Huang, Ying > Thanks. > >> >> > and thus be offlined while it's still being used by the >> > do_pages_stat_array(). >> >> "offline" seems a possible problem.
On 2022/3/7 15:42, Huang, Ying wrote: > Muchun Song <songmuchun@bytedance.com> writes: > >> On Mon, Mar 7, 2022 at 1:22 PM Huang, Ying <ying.huang@intel.com> wrote: >>> >>> Miaohe Lin <linmiaohe@huawei.com> writes: >>> >>>> When follow_page peeks a page, the page could be reclaimed under heavy >>>> memory pressure >>> >>> I don't think that memory pressure and reclaiming will be an issue. >> >> I think he means a page first to be reclaimed then to be offline >> could encounter this issue and reclaiming is a precondition. > > I don't think reclaiming is a precondition. It seems possible that the > virtual page is migrated, then the physical page is offlined. > What I indeed mean is a page could first be reclaimed, migrated and so on. And then be offlined. Sorry for confusing. Thanks both of you. > Best Regards, > Huang, Ying > >> Thanks. >> >>> >>>> and thus be offlined while it's still being used by the >>>> do_pages_stat_array(). >>> >>> "offline" seems a possible problem. > . >
diff --git a/mm/migrate.c b/mm/migrate.c index 7b1c0b988234..98a968e6f465 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1788,13 +1788,18 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, goto set_status; /* FOLL_DUMP to ignore special (like zero) pages */ - page = follow_page(vma, addr, FOLL_DUMP); + page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); err = PTR_ERR(page); if (IS_ERR(page)) goto set_status; - err = page ? page_to_nid(page) : -ENOENT; + if (page) { + err = page_to_nid(page); + put_page(page); + } else { + err = -ENOENT; + } set_status: *status = err;
When follow_page peeks a page, the page could be reclaimed under heavy memory pressure and thus be offlined while it's still being used by the do_pages_stat_array(). Use FOLL_GET to hold the page refcnt to fix this potential issue. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/migrate.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)