On Thu, Nov 23, 2023 at 07:11:19PM +0000, Ryan Roberts wrote: > Hi, > > I'm not sure I've 100% understood the crossover between this series and my > work > to support arm64's contpte mappings generally for anonymous and file-backed > memory.
No worry, there's no confliction. If you worked on that it's only be something nice on top. Also, I'm curious if you have performance numbers, because I'm going to do some test for hugetlb cont_ptes (which is only the current plan), and if you got those it'll be a great baseline for me, because it should be similar in you case even though the goal is slightly different. > > My approach is to transparently use contpte mappings when core-mm request pte > mappings that meet the requirements; and its all based around intercepting the > normal (non-hugetlb) helpers (e.g. set_ptes(), ptep_get() and friends). There > is > no semantic change to the core-mm. See [1]. It relies on 1) the page cache > using > large folios and 2) my "small-sized THP" series which starts using arbitrary > sized large folios for anonymous memory [2]. > > If I've understood this conversation correctly there is an object called > hugepd, > which today is only supported by powerpc, but which could allow the core-mm to > control the mapping granularity? I can see some value in exposing that control > to core-mm in the (very) long term. For me it's needed immediately, because hugetlb_follow_page_mask() will be gone after the last patch. > > [1] https://lore.kernel.org/all/20231115163018.1303287-1-ryan.robe...@arm.com/ > [2] > https://lore.kernel.org/linux-mm/20231115132734.931023-1-ryan.robe...@arm.com/ AFAICT you haven't yet worked on gup then, after I glimpsed the above series. It's a matter of whether one follow_page_mask() call can fetch more than one page* for a cont_pte entry on aarch64 for a large non-hugetlb folio (and if this series lands, it'll be the same to hugetlb or non-hugetlb). Now the current code can only fetch one page I think. Thanks, -- Peter Xu
