On Wed, Oct 20, 2021 at 10:09 AM Joao Martins <joao.m.martins@xxxxxxxxxx> wrote: > > On 10/19/21 20:21, Dan Williams wrote: > > On Tue, Oct 19, 2021 at 9:02 AM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > >> > >> On Tue, Oct 19, 2021 at 04:13:34PM +0100, Joao Martins wrote: > >>> On 10/19/21 00:06, Jason Gunthorpe wrote: > >>>> On Mon, Oct 18, 2021 at 12:37:30PM -0700, Dan Williams wrote: > >>>> > >>>>>> device-dax uses PUD, along with TTM, they are the only places. I'm not > >>>>>> sure TTM is a real place though. > >>>>> > >>>>> I was setting device-dax aside because it can use Joao's changes to > >>>>> get compound-page support. > >>>> > >>>> Ideally, but that ideas in that patch series have been floating around > >>>> for a long time now.. > >>>> > >>> The current status of the series misses a Rb on patches 6,7,10,12-14. > >>> Well, patch 8 too should now drop its tag, considering the latest > >>> discussion. > >>> > >>> If it helps moving things forward I could split my series further into: > >>> > >>> 1) the compound page introduction (patches 1-7) of my aforementioned series > >>> 2) vmemmap deduplication for memory gains (patches 9-14) > >>> 3) gup improvements (patch 8 and gup-slow improvements) > >> > >> I would split it, yes.. > >> > >> I think we can see a general consensus that making compound_head/etc > >> work consistently with how THP uses it will provide value and > >> opportunity for optimization going forward. > >> > > I'll go do that. Meanwhile, I'll wait a couple days for Dan to review the > dax subsystem patches (6 & 7), or otherwise send them over. > > >>> Whats the benefit between preventing longterm at start > >>> versus only after mounting the filesystem? Or is the intended future purpose > >>> to pass more context into an holder potential future callback e.g. nack longterm > >>> pins on a page basis? > >> > >> I understood Dan's remark that the device-dax path allows > >> FOLL_LONGTERM and the FSDAX path does not ? > >> > >> Which, IIRC, today is signaled basd on vma properties and in all cases > >> fast-gup is denied. > > > > Yeah, I forgot that 7af75561e171 eliminated any possibility of > > longterm-gup-fast for device-dax, let's not disturb that status quo. > > > I am slightly confused by this comment -- the status quo is what we are > questioning here -- And we talked about changing that in the past too > (thread below), that longterm-gup-fast was an oversight that that commit > was only applicable to fsdax. [Maybe this is just my english confusion] No, you have it correct. However that "regression" has gone unnoticed, so unless there is data showing that gup-fast on device-dax is critical for longterm page pinning workflows I'm ok for longterm to continue to trigger gup-slow.
