| Message ID | 20230216064726.2724268-1-pcc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kasan: call clear_page with a match-all tag instead of changing page tag | expand |
On Wed, Feb 15, 2023 at 10:47:26PM -0800, Peter Collingbourne wrote: > Instead of changing the page's tag solely in order to obtain a pointer > with a match-all tag and then changing it back again, just convert the > pointer that we get from kmap_atomic() into one with a match-all tag > before passing it to clear_page(). > > On a certain microarchitecture, this has been observed to cause a > measurable improvement in microbenchmark performance, presumably as a > result of being able to avoid the atomic operations on the page tag. Yeah, this would likely break the write streaming mode on some ARM CPUs. > Signed-off-by: Peter Collingbourne <pcc@google.com> > Link: https://linux-review.googlesource.com/id/I0249822cc29097ca7a04ad48e8eb14871f80e711 > --- > include/linux/highmem.h | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index 44242268f53b..bbfa546dd602 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -245,12 +245,10 @@ static inline void clear_highpage(struct page *page) > > static inline void clear_highpage_kasan_tagged(struct page *page) > { > - u8 tag; > + void *kaddr = kmap_atomic(page); > > - tag = page_kasan_tag(page); > - page_kasan_tag_reset(page); > - clear_highpage(page); > - page_kasan_tag_set(page, tag); > + clear_page(kasan_reset_tag(kaddr)); > + kunmap_atomic(kaddr); > } Please don't add kmap_atomic() back. See commit d2c20e51e396 ("mm/highmem: remove deprecated kmap_atomic"). I'd duplicate the clear_highpage() logic in here and call clear_page() directly on the address with the kasan tag reset.
On Thu, Feb 16, 2023 at 6:27 AM Catalin Marinas <catalin.marinas@arm.com> wrote: > > On Wed, Feb 15, 2023 at 10:47:26PM -0800, Peter Collingbourne wrote: > > Instead of changing the page's tag solely in order to obtain a pointer > > with a match-all tag and then changing it back again, just convert the > > pointer that we get from kmap_atomic() into one with a match-all tag > > before passing it to clear_page(). > > > > On a certain microarchitecture, this has been observed to cause a > > measurable improvement in microbenchmark performance, presumably as a > > result of being able to avoid the atomic operations on the page tag. > > Yeah, this would likely break the write streaming mode on some ARM CPUs. > > > Signed-off-by: Peter Collingbourne <pcc@google.com> > > Link: https://linux-review.googlesource.com/id/I0249822cc29097ca7a04ad48e8eb14871f80e711 > > --- > > include/linux/highmem.h | 8 +++----- > > 1 file changed, 3 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > > index 44242268f53b..bbfa546dd602 100644 > > --- a/include/linux/highmem.h > > +++ b/include/linux/highmem.h > > @@ -245,12 +245,10 @@ static inline void clear_highpage(struct page *page) > > > > static inline void clear_highpage_kasan_tagged(struct page *page) > > { > > - u8 tag; > > + void *kaddr = kmap_atomic(page); > > > > - tag = page_kasan_tag(page); > > - page_kasan_tag_reset(page); > > - clear_highpage(page); > > - page_kasan_tag_set(page, tag); > > + clear_page(kasan_reset_tag(kaddr)); > > + kunmap_atomic(kaddr); > > } > > Please don't add kmap_atomic() back. See commit d2c20e51e396 > ("mm/highmem: remove deprecated kmap_atomic"). I'd duplicate the > clear_highpage() logic in here and call clear_page() directly on the > address with the kasan tag reset. Right, that's how I originally developed this patch. As you might have guessed, I was developing against a stable kernel, so I was copying the old version of clear_highpage(). Done in v2. Peter
diff --git a/include/linux/highmem.h b/include/linux/highmem.h index 44242268f53b..bbfa546dd602 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -245,12 +245,10 @@ static inline void clear_highpage(struct page *page) static inline void clear_highpage_kasan_tagged(struct page *page) { - u8 tag; + void *kaddr = kmap_atomic(page); - tag = page_kasan_tag(page); - page_kasan_tag_reset(page); - clear_highpage(page); - page_kasan_tag_set(page, tag); + clear_page(kasan_reset_tag(kaddr)); + kunmap_atomic(kaddr); } #ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
Instead of changing the page's tag solely in order to obtain a pointer with a match-all tag and then changing it back again, just convert the pointer that we get from kmap_atomic() into one with a match-all tag before passing it to clear_page(). On a certain microarchitecture, this has been observed to cause a measurable improvement in microbenchmark performance, presumably as a result of being able to avoid the atomic operations on the page tag. Signed-off-by: Peter Collingbourne <pcc@google.com> Link: https://linux-review.googlesource.com/id/I0249822cc29097ca7a04ad48e8eb14871f80e711 --- include/linux/highmem.h | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)