| Message ID | 20220815010349.432313-2-haiyue.wang@intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | fix follow_page related issues | expand |
Haiyue Wang <haiyue.wang@intel.com> writes: > Not all huge page APIs support FOLL_GET option, so the __NR_move_pages move_pages() is a syscall, so you can just call it move_pages(), or move_pages() syscall. > will fail to get the page node information for huge page. ~~~~~~~~~ some huge pages? > This is an temporary solution to mitigate the racing fix. Why is it "racing fix"? This isn't a race condition fix. Best Regards, Huang, Ying > After supporting follow huge page by FOLL_GET is done, this fix can be > reverted safely. > > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") > Signed-off-by: Haiyue Wang <haiyue.wang@intel.com> [snip]
> -----Original Message----- > From: Huang, Ying <ying.huang@intel.com> > Sent: Monday, August 15, 2022 09:59 > To: Wang, Haiyue <haiyue.wang@intel.com> > Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; akpm@linux-foundation.org; david@redhat.com; > linmiaohe@huawei.com; songmuchun@bytedance.com; naoya.horiguchi@linux.dev; alex.sierra@amd.com > Subject: Re: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page > > Haiyue Wang <haiyue.wang@intel.com> writes: > > > Not all huge page APIs support FOLL_GET option, so the __NR_move_pages > > move_pages() is a syscall, so you can just call it move_pages(), or > move_pages() syscall. The application meets the issue, use the bellow function: syscall (__NR_move_pages, 0, n_pages, ptr, 0, status, 0) So I used it directly in the commit. "move_pages() syscall" is better. Will update latter. > > > will fail to get the page node information for huge page. > ~~~~~~~~~ > some huge pages? OK. > > > This is an temporary solution to mitigate the racing fix. > > Why is it "racing fix"? This isn't a race condition fix. The 'Fixes' commit is about race condition fix. How about " his is an temporary solution to mitigate the side effect Of the race condition fix" > > Best Regards, > Huang, Ying > > > After supporting follow huge page by FOLL_GET is done, this fix can be > > reverted safely. > > > > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") > > Signed-off-by: Haiyue Wang <haiyue.wang@intel.com> > > [snip]
> -----Original Message----- > From: Wang, Haiyue > Sent: Monday, August 15, 2022 10:11 > To: Huang, Ying <ying.huang@intel.com> > Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; akpm@linux-foundation.org; david@redhat.com; > linmiaohe@huawei.com; songmuchun@bytedance.com; naoya.horiguchi@linux.dev; alex.sierra@amd.com > Subject: RE: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page > > > -----Original Message----- > > From: Huang, Ying <ying.huang@intel.com> > > Sent: Monday, August 15, 2022 09:59 > > To: Wang, Haiyue <haiyue.wang@intel.com> > > Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; akpm@linux-foundation.org; david@redhat.com; > > linmiaohe@huawei.com; songmuchun@bytedance.com; naoya.horiguchi@linux.dev; alex.sierra@amd.com > > Subject: Re: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page > > > > Haiyue Wang <haiyue.wang@intel.com> writes: > > > > > > > This is an temporary solution to mitigate the racing fix. > > > > Why is it "racing fix"? This isn't a race condition fix. > > The 'Fixes' commit is about race condition fix. > > How about " his is an temporary solution to mitigate the side effect > Of the race condition fix" Try to add more words to make things clean: "This is an temporary solution to mitigate the side effect of the race condition fix by calling follow_page() with FOLL_GET set." > > > > > Best Regards, > > Huang, Ying > > > > > After supporting follow huge page by FOLL_GET is done, this fix can be > > > reverted safely. > > > > > > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") > > > Signed-off-by: Haiyue Wang <haiyue.wang@intel.com> > > > > [snip]
"Wang, Haiyue" <haiyue.wang@intel.com> writes: >> -----Original Message----- >> From: Wang, Haiyue >> Sent: Monday, August 15, 2022 10:11 >> To: Huang, Ying <ying.huang@intel.com> >> Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; akpm@linux-foundation.org; david@redhat.com; >> linmiaohe@huawei.com; songmuchun@bytedance.com; naoya.horiguchi@linux.dev; alex.sierra@amd.com >> Subject: RE: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page >> >> > -----Original Message----- >> > From: Huang, Ying <ying.huang@intel.com> >> > Sent: Monday, August 15, 2022 09:59 >> > To: Wang, Haiyue <haiyue.wang@intel.com> >> > Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; akpm@linux-foundation.org; david@redhat.com; >> > linmiaohe@huawei.com; songmuchun@bytedance.com; naoya.horiguchi@linux.dev; alex.sierra@amd.com >> > Subject: Re: [PATCH v3 1/2] mm: migration: fix the FOLL_GET failure on following huge page >> > >> > Haiyue Wang <haiyue.wang@intel.com> writes: >> > > > >> > >> > > This is an temporary solution to mitigate the racing fix. >> > >> > Why is it "racing fix"? This isn't a race condition fix. >> >> The 'Fixes' commit is about race condition fix. >> >> How about " his is an temporary solution to mitigate the side effect >> Of the race condition fix" > > Try to add more words to make things clean: > > "This is an temporary solution to mitigate the side effect of the race > condition fix by calling follow_page() with FOLL_GET set." Looks good to me. Thanks! Best Regards, Huang, Ying >> >> > >> > Best Regards, >> > Huang, Ying >> > >> > > After supporting follow huge page by FOLL_GET is done, this fix can be >> > > reverted safely. >> > > >> > > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") >> > > Signed-off-by: Haiyue Wang <haiyue.wang@intel.com> >> > >> > [snip]
diff --git a/mm/migrate.c b/mm/migrate.c index 6a1597c92261..581dfaad9257 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1848,6 +1848,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, for (i = 0; i < nr_pages; i++) { unsigned long addr = (unsigned long)(*pages); + unsigned int foll_flags = FOLL_DUMP; struct vm_area_struct *vma; struct page *page; int err = -EFAULT; @@ -1856,8 +1857,12 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, if (!vma) goto set_status; + /* Not all huge page follow APIs support 'FOLL_GET' */ + if (!is_vm_hugetlb_page(vma)) + foll_flags |= FOLL_GET; + /* FOLL_DUMP to ignore special (like zero) pages */ - page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); + page = follow_page(vma, addr, foll_flags); err = PTR_ERR(page); if (IS_ERR(page)) @@ -1865,7 +1870,8 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, if (page && !is_zone_device_page(page)) { err = page_to_nid(page); - put_page(page); + if (foll_flags & FOLL_GET) + put_page(page); } else { err = -ENOENT; }
Not all huge page APIs support FOLL_GET option, so the __NR_move_pages will fail to get the page node information for huge page. This is an temporary solution to mitigate the racing fix. After supporting follow huge page by FOLL_GET is done, this fix can be reverted safely. Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") Signed-off-by: Haiyue Wang <haiyue.wang@intel.com> --- mm/migrate.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)