On Mon 11-09-23 18:49:06, zhaoyang.huang wrote: > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > There will be redundant clear page within vma_alloc_zeroed_movable_folio > when CONFIG_INIT_ON_ALLOC_DEFAULT_ON is on. Remove it by judging related > configs. Thanks for spotting this. I suspect this is a fix based on a code review rather than a real performance issue, right? It is always good to mention that. From a very quick look it seems that many architectures just definte vma_alloc_zeroed_movable_folio to use __GFP_ZERO so they are not affected by this. This means that only a subset of architectures are really affected. This is an important information as well. Finally I think it would be more appropriate to mention that the double initialization is done when init_on_alloc is enabled rather than referring to the above config option which only controls whether the functionality is enabled by default. I would rephrase as follows: Many architectures (alpha, arm64, ia64, m68k s390, x86) define their own vma_alloc_zeroed_movable_folio implementations which use __GFP_ZERO for the page allocation. Those which rely on the default implementation, however, would currently go through the initialization twice (oce in the page allocator and second in vma_alloc_zeroed_movable_folio) if init_on_alloc is enabled though. Fix this by checking want_init_on_alloc before calling clear_user_highpage. > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> With the changelog updates Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! > --- > include/linux/highmem.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index 99c474de800d..3926f8414729 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -227,7 +227,7 @@ struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma, > struct folio *folio; > > folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr, false); > - if (folio) > + if (folio && !want_init_on_alloc(GFP_HIGHUSER_MOVABLE)) > clear_user_highpage(&folio->page, vaddr); > > return folio; > -- > 2.25.1 -- Michal Hocko SUSE Labs
