| Message ID | 20220816130553.31406-4-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | A few fixup patches for hugetlb | expand |
On 08/16/22 21:05, Miaohe Lin wrote: > When huge_add_to_page_cache() fails, the page is freed directly without > calling restore_reserve_on_error() to restore reserve for newly allocated > pages not in page cache. Fix this by calling restore_reserve_on_error() > when huge_add_to_page_cache fails. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/hugetlb.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index ff991e5bdf1f..b69d7808f457 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5603,6 +5603,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, > if (vma->vm_flags & VM_MAYSHARE) { > int err = huge_add_to_page_cache(page, mapping, idx); > if (err) { > + restore_reserve_on_error(h, vma, haddr, page); Hmmmm. I was going to comment that restore_reserve_on_error would not handle the situation where 'err == -EEXIST' below. This is because it implies we raced with someone else that added the page to the cache. And, that other allocation, not this one, consumed the reservation. However, I am not sure how that could be possible? The hugetlb fault mutex (which we hold) must be held to add a page to the page cache. Searching git history I see that code was added (or at least existed) before the hugetlb fault mutex was introduced. So, I believe that check for -EEXIST and retry can go. With that said, restore_reserve_on_error can be called here. But, let's look into removing that err == -EEXIST check to avoid confusion.
On 2022/8/17 7:31, Mike Kravetz wrote: > On 08/16/22 21:05, Miaohe Lin wrote: >> When huge_add_to_page_cache() fails, the page is freed directly without >> calling restore_reserve_on_error() to restore reserve for newly allocated >> pages not in page cache. Fix this by calling restore_reserve_on_error() >> when huge_add_to_page_cache fails. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> mm/hugetlb.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index ff991e5bdf1f..b69d7808f457 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -5603,6 +5603,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, >> if (vma->vm_flags & VM_MAYSHARE) { >> int err = huge_add_to_page_cache(page, mapping, idx); >> if (err) { >> + restore_reserve_on_error(h, vma, haddr, page); > > Hmmmm. I was going to comment that restore_reserve_on_error would not handle > the situation where 'err == -EEXIST' below. This is because it implies we > raced with someone else that added the page to the cache. And, that other Thanks for pointing this out. > allocation, not this one, consumed the reservation. However, I am not sure > how that could be possible? The hugetlb fault mutex (which we hold) > must be held to add a page to the page cache. > > Searching git history I see that code was added (or at least existed) before > the hugetlb fault mutex was introduced. So, I believe that check for -EEXIST > and retry can go. Agree with you. All call sites of huge_add_to_page_cache is protected by hugetlb fault mutex. > > With that said, restore_reserve_on_error can be called here. But, let's > look into removing that err == -EEXIST check to avoid confusion. Will do it in next version. Many thanks for your review and comment. Thanks, Miaohe Lin
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index ff991e5bdf1f..b69d7808f457 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5603,6 +5603,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, if (vma->vm_flags & VM_MAYSHARE) { int err = huge_add_to_page_cache(page, mapping, idx); if (err) { + restore_reserve_on_error(h, vma, haddr, page); put_page(page); if (err == -EEXIST) goto retry;
When huge_add_to_page_cache() fails, the page is freed directly without calling restore_reserve_on_error() to restore reserve for newly allocated pages not in page cache. Fix this by calling restore_reserve_on_error() when huge_add_to_page_cache fails. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/hugetlb.c | 1 + 1 file changed, 1 insertion(+)