Re: [PATCH v2 2/6] mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page
From: Michal Hocko <mhocko@suse.com>
Date: 2021-01-06 16:36:03
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On Wed 06-01-21 16:47:35, Muchun Song wrote:
Because we only can isolate a active page via isolate_huge_page() and hugetlbfs_fallocate() forget to mark it as active, we cannot isolate and migrate those pages.
I've little bit hard time to understand this initially and had to dive into the code to make sense of it. I would consider the following wording easier to grasp. Feel free to reuse if you like. " If a new hugetlb page is allocated during fallocate it will not be marked as active (set_page_huge_active) which will result in a later isolate_huge_page failure when the page migration code would like to move that page. Such a failure would be unexpected and wrong. " Now to the fix. I believe that this patch shows that the set_page_huge_active is just too subtle. Is there any reason why we cannot make all freshly allocated huge pages active by default?
quoted hunk ↗ jump to hunk
Only export set_page_huge_active, just leave clear_page_huge_active as static. Because there are no external users. Fixes: 70c3547e36f5 (hugetlbfs: add hugetlbfs_fallocate()) Signed-off-by: Muchun Song <redacted> --- fs/hugetlbfs/inode.c | 3 ++- include/linux/hugetlb.h | 2 ++ mm/hugetlb.c | 2 +- 3 files changed, 5 insertions(+), 2 deletions(-)diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index b5c109703daa..21c20fd5f9ee 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c@@ -735,9 +735,10 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset, mutex_unlock(&hugetlb_fault_mutex_table[hash]); + set_page_huge_active(page); /* * unlock_page because locked by add_to_page_cache() - * page_put due to reference from alloc_huge_page() + * put_page() due to reference from alloc_huge_page() */ unlock_page(page); put_page(page);diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index ebca2ef02212..b5807f23caf8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h@@ -770,6 +770,8 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma, } #endif +void set_page_huge_active(struct page *page); + #else /* CONFIG_HUGETLB_PAGE */ struct hstate {};diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 1f3bf1710b66..4741d60f8955 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c@@ -1348,7 +1348,7 @@ bool page_huge_active(struct page *page) } /* never called for tail page */ -static void set_page_huge_active(struct page *page) +void set_page_huge_active(struct page *page) { VM_BUG_ON_PAGE(!PageHeadHuge(page), page); SetPagePrivate(&page[1]);-- 2.11.0
-- Michal Hocko SUSE Labs