| Message ID | ZVzQkTueDRSJ76me@tuxmaker.boeblingen.de.ibm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] pgtable: do not expose _refcount field via ptdesc | expand |
On Tue, Nov 21, 2023 at 04:45:21PM +0100, Alexander Gordeev wrote: > Since commit d08d4e7cd6bf ("s390/mm: use full 4KB page for 2KB PTE") > _refcount field is not used for fragmented page tracking on s390 and > there is no other code left that accesses this field explicitly. > > Suggested-by: Heiko Carstens <hca@linux.ibm.com> > Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com> > --- > include/linux/mm_types.h | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 957ce38768b2..ce0cfc6e4d94 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -401,11 +401,11 @@ FOLIO_MATCH(compound_head, _head_2a); > * @pmd_huge_pte: Protected by ptdesc->ptl, used for THPs. > * @__page_mapping: Aliases with page->mapping. Unused for page tables. > * @pt_mm: Used for x86 pgds. > - * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only. > + * @pt_frag_refcount: For fragmented page table tracking. Powerpc only. > * @_pt_pad_2: Padding to ensure proper alignment. > * @ptl: Lock for the page table. > * @__page_type: Same as page->page_type. Unused for page tables. > - * @_refcount: Same as page refcount. Used for s390 page tables. > + * @_pt_pad_3: Padding that aliases with page's refcount. I like updating the documentation, but I'd rather see _refcount renamed to __page_refcount similar to the other unused page fields. _pt_pad_* is used for variables that aren't present in struct page (and are required for padding). > * @pt_memcg_data: Memcg data. Tracked for page tables here. > * > * This struct overlays struct page for now. Do not modify without a good > @@ -438,7 +438,7 @@ struct ptdesc { > #endif > }; > unsigned int __page_type; > - atomic_t _refcount; > + unsigned int _pt_pad_3; > #ifdef CONFIG_MEMCG > unsigned long pt_memcg_data; > #endif > @@ -452,7 +452,6 @@ TABLE_MATCH(compound_head, _pt_pad_1); > TABLE_MATCH(mapping, __page_mapping); > TABLE_MATCH(rcu_head, pt_rcu_head); > TABLE_MATCH(page_type, __page_type); > -TABLE_MATCH(_refcount, _refcount); Its still a good idea to keep this check. In the case of !CONFIG_MEMCG, _refcount is the last variable of ptdesc and if some change were to happen that caused it to be misaligned we will want to know. > #ifdef CONFIG_MEMCG > TABLE_MATCH(memcg_data, pt_memcg_data); > #endif > -- > 2.39.2 > >
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 957ce38768b2..ce0cfc6e4d94 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -401,11 +401,11 @@ FOLIO_MATCH(compound_head, _head_2a); * @pmd_huge_pte: Protected by ptdesc->ptl, used for THPs. * @__page_mapping: Aliases with page->mapping. Unused for page tables. * @pt_mm: Used for x86 pgds. - * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only. + * @pt_frag_refcount: For fragmented page table tracking. Powerpc only. * @_pt_pad_2: Padding to ensure proper alignment. * @ptl: Lock for the page table. * @__page_type: Same as page->page_type. Unused for page tables. - * @_refcount: Same as page refcount. Used for s390 page tables. + * @_pt_pad_3: Padding that aliases with page's refcount. * @pt_memcg_data: Memcg data. Tracked for page tables here. * * This struct overlays struct page for now. Do not modify without a good @@ -438,7 +438,7 @@ struct ptdesc { #endif }; unsigned int __page_type; - atomic_t _refcount; + unsigned int _pt_pad_3; #ifdef CONFIG_MEMCG unsigned long pt_memcg_data; #endif @@ -452,7 +452,6 @@ TABLE_MATCH(compound_head, _pt_pad_1); TABLE_MATCH(mapping, __page_mapping); TABLE_MATCH(rcu_head, pt_rcu_head); TABLE_MATCH(page_type, __page_type); -TABLE_MATCH(_refcount, _refcount); #ifdef CONFIG_MEMCG TABLE_MATCH(memcg_data, pt_memcg_data); #endif
Since commit d08d4e7cd6bf ("s390/mm: use full 4KB page for 2KB PTE") _refcount field is not used for fragmented page tracking on s390 and there is no other code left that accesses this field explicitly. Suggested-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com> --- include/linux/mm_types.h | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)