On Wed 16-01-19 04:30:18, Matthew Wilcox wrote: > On Wed, Jan 16, 2019 at 07:57:03AM +0100, Michal Hocko wrote: > > On Wed 16-01-19 11:51:32, Anshuman Khandual wrote: > > > All architectures have been defining their own PGALLOC_GFP as (GFP_KERNEL > > > | > > > __GFP_ZERO) and using it for allocating page table pages. This causes some > > > code duplication which can be easily avoided. GFP_KERNEL allocated and > > > cleared out pages (__GFP_ZERO) are required for page tables on any given > > > architecture. This creates a new generic GFP flag flag which can be used > > > for any page table page allocation. Does not cause any functional change. > > > > > > GFP_PGTABLE is being added into include/asm-generic/pgtable.h which is the > > > generic page tabe header just to prevent it's potential misuse as a > > > general > > > allocation flag if included in include/linux/gfp.h. > > > > I haven't reviewed the patch yet but I am wondering whether this is > > really worth it without going all the way down to unify the common code > > and remove much more code duplication. Or is this not possible for some > > reason? > > Exactly what I suggested doing in response to v1. > > Also, the approach taken here is crazy. x86 has a feature that no other > architecture has bothered to implement yet -- accounting page tables > to the process. Yet instead of spreading that goodness to all other > architectures, Anshuman has gone to more effort to avoid doing that.
Yes, I believe the only reason this is x86 only is that each arch would have to be tweaked separately. So a cleanup in _that_ regard would be helpful. There is no real reason to have ptes accounted only for x86. There might be some exceptions but well, our asm-generic allows to opt in for generic implementation or override it with a special one. The later should be an exception rather than the rule. -- Michal Hocko SUSE Labs
