Messages in this thread | | | Date | Fri, 22 Jan 2021 12:13:35 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH 0/1] mm: Optimizing hugepage zeroing in arm64 |
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On Thu, Jan 21, 2021 at 06:59:37PM +0000, Robin Murphy wrote: > On 2021-01-21 17:46, Will Deacon wrote: > > On Thu, Jan 21, 2021 at 10:21:50PM +0530, Prathu Baronia wrote: > > > This patch removes the unnecessary kmap calls in the hugepage zeroing path and > > > improves the timing by 62%. > > > > > > I had proposed a similar change in Apr-May'20 timeframe in memory.c where I > > > proposed to clear out a hugepage by directly calling a memset over the whole > > > hugepage but got the opposition that the change was not architecturally neutral. > > > > > > Upon revisiting this now I see significant improvement by removing around 2k > > > barrier calls from the zeroing path. So hereby I propose an arm64 specific > > > definition of clear_user_highpage(). > > > > Given that barrier() is purely a thing for the compiler, wouldn't the same > > change yield a benefit on any other architecture without HIGHMEM? In which > > case, I think this sort of change belongs in the core code if it's actually > > worthwhile. > > I would have thought it's more the constant manipulation of the preempt and > pagefault counts, rather than the compiler barriers between them, that has > the impact. Either way, if arm64 doesn't need to be atomic WRT preemption > when clearing parts of hugepages then I also can't imagine that anyone else > (at least for !HIGHMEM) would either.
I thought the kmap_local stuff was supposed to fix this unnecessary preemption disabling on 64-bit architectures:
https://lwn.net/Articles/836144/
I guess it's not there yet.
-- Catalin
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