On Tue, Aug 24, 2021 at 04:38:03PM +0000, Edgecombe, Rick P wrote: > On Tue, 2021-08-24 at 16:02 +0300, Mike Rapoport wrote: > > > We probably want to exclude GFP_ATOMIC before calling into CPA > > > unless > > > debug page alloc is on, because it may need to split and sleep for > > > the > > > allocation. There is a page table allocation with GFP_ATOMIC passed > > > actually. > > > > Looking at the callers of alloc_low_pages() it seems that GFP_ATOMIC > > there > > is stale... > > Well two actually, there is also spp_getpage(). I tried to determine if > that was also stale but wasn't confident. There were a lot of paths in. It's also used at init and during memory hotplug, so I really doubt it needs GFP_ATOMIC. > > > In my next series of this I added support for GFP_ATOMIC to this > > > code, > > > but that solution should only work for permission changing grouped > > > page > > > allocators in the protected page tables case where the direct map > > > tables are handled differently. As a general solution though > > > (that's > > > the long term intention right?), GFP_ATOMIC might deserve some > > > consideration. > > > > ... but for the general solution GFP_ATOMIC indeed deserves some > > consideration. > > > > > The other thing is we probably don't want to clean out the atomic > > > reserves and add them to a cache just for one page. I opted to just > > > convert one page in the GFP_ATOMIC case. > > > > Do you mean to allocate one page in GFP_ATOMIC case and bypass high > > order > > allocation? > > But the CPA split is still necessary here, isn't it? > > Yes, grabs one atomic page and fragments it in the case of no pages in > the grouped page cache. The CPA split is necessary still, but it should > be ok because of the special way direct map page table allocations are > handled for pks tables. Has not been reviewed by anyone yet, and > wouldn't work as a general solution anyway. -- Sincerely yours, Mike.
