| Message ID | 20210908102648.2326917-2-liuyuntao10@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | fix judgment error in shmem_is_huge() | expand |
On Wed, Sep 08, 2021 at 06:26:48PM +0800, Liu Yuntao wrote: > In the case of SHMEM_HUGE_WITHIN_SIZE, the page index is not rounded > up correctly. When the page index points to the first page in a huge > page, round_up() cannot bring it to the end of the huge page, but > to the end of the previous one. > > an example: > HPAGE_PMD_NR on my machine is 512(2 MB huge page size). > After allcoating a 3000 KB buffer, I access it at location 2050 KB. > In shmem_is_huge(), the corresponding index happens to be 512. > After rounded up by HPAGE_PMD_NR, it will still be 512 which is > smaller than i_size, and shmem_is_huge() will return true. > As a result, my buffer takes an additional huge page, and that > shouldn't happen when shmem_enabled is set to within_size. > > Fixes: f3f0e1d2150b2b ("khugepaged: add support of collapse for tmpfs/shmem pages") > Signed-off-by: Liu Yuntao <liuyuntao10@huawei.com> > --- > mm/shmem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 88742953532c..5747572859d1 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -490,7 +490,7 @@ bool shmem_is_huge(struct vm_area_struct *vma, > case SHMEM_HUGE_ALWAYS: > return true; > case SHMEM_HUGE_WITHIN_SIZE: > - index = round_up(index, HPAGE_PMD_NR); > + index = round_up(index + 1, HPAGE_PMD_NR); > i_size = round_up(i_size_read(inode), PAGE_SIZE); > if (i_size >= HPAGE_PMD_SIZE && (i_size >> PAGE_SHIFT) >= index) With the change, the condition can be simplified to if (i_size >> PAGE_SHIFT >= index) right? > return true; > -- > 2.23.0 >
On Wed, 8 Sep 2021 17:58:44 +0300, Kirill A. Shutemov wrote: > On Wed, Sep 08, 2021 at 06:26:48PM +0800, Liu Yuntao wrote: > > In the case of SHMEM_HUGE_WITHIN_SIZE, the page index is not rounded > > up correctly. When the page index points to the first page in a huge > > page, round_up() cannot bring it to the end of the huge page, but > > to the end of the previous one. > > > > an example: > > HPAGE_PMD_NR on my machine is 512(2 MB huge page size). > > After allcoating a 3000 KB buffer, I access it at location 2050 KB. > > In shmem_is_huge(), the corresponding index happens to be 512. > > After rounded up by HPAGE_PMD_NR, it will still be 512 which is > > smaller than i_size, and shmem_is_huge() will return true. > > As a result, my buffer takes an additional huge page, and that > > shouldn't happen when shmem_enabled is set to within_size. > > > > Fixes: f3f0e1d2150b2b ("khugepaged: add support of collapse for tmpfs/shmem pages") > > Signed-off-by: Liu Yuntao <liuyuntao10@huawei.com> > > --- > > mm/shmem.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/shmem.c b/mm/shmem.c > > index 88742953532c..5747572859d1 100644 > > --- a/mm/shmem.c > > +++ b/mm/shmem.c > > @@ -490,7 +490,7 @@ bool shmem_is_huge(struct vm_area_struct *vma, > > case SHMEM_HUGE_ALWAYS: > > return true; > > case SHMEM_HUGE_WITHIN_SIZE: > > - index = round_up(index, HPAGE_PMD_NR); > > + index = round_up(index + 1, HPAGE_PMD_NR); > > i_size = round_up(i_size_read(inode), PAGE_SIZE); > > if (i_size >= HPAGE_PMD_SIZE && (i_size >> PAGE_SHIFT) >= index) > > With the change, the condition can be simplified to > > if (i_size >> PAGE_SHIFT >= index) > > right? Yes, will add it. > > > return true; > > -- > > 2.23.0 > > > > -- > Kirill A. Shutemov
diff --git a/mm/shmem.c b/mm/shmem.c index 88742953532c..5747572859d1 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -490,7 +490,7 @@ bool shmem_is_huge(struct vm_area_struct *vma, case SHMEM_HUGE_ALWAYS: return true; case SHMEM_HUGE_WITHIN_SIZE: - index = round_up(index, HPAGE_PMD_NR); + index = round_up(index + 1, HPAGE_PMD_NR); i_size = round_up(i_size_read(inode), PAGE_SIZE); if (i_size >= HPAGE_PMD_SIZE && (i_size >> PAGE_SHIFT) >= index) return true;
In the case of SHMEM_HUGE_WITHIN_SIZE, the page index is not rounded up correctly. When the page index points to the first page in a huge page, round_up() cannot bring it to the end of the huge page, but to the end of the previous one. an example: HPAGE_PMD_NR on my machine is 512(2 MB huge page size). After allcoating a 3000 KB buffer, I access it at location 2050 KB. In shmem_is_huge(), the corresponding index happens to be 512. After rounded up by HPAGE_PMD_NR, it will still be 512 which is smaller than i_size, and shmem_is_huge() will return true. As a result, my buffer takes an additional huge page, and that shouldn't happen when shmem_enabled is set to within_size. Fixes: f3f0e1d2150b2b ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Liu Yuntao <liuyuntao10@huawei.com> --- mm/shmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)