Re: API for setting multiple PTEs at once

Alexandre Ghiti
2023-02-08T11:23:53Z

Hi Matthew,

On 2/7/23 21:27, Matthew Wilcox wrote:
> On Thu, Feb 02, 2023 at 09:14:23PM +0000, Matthew Wilcox wrote:
>> For those of you not subscribed, linux-mm is currently discussing
>> how best to handle page faults on large folios. I simply made it work
>> when adding large folio support. Now Yin Fengwei is working on
>> making it fast.
> OK, here's an actual implementation:
>
> https://lore.kernel.org/linux-mm/20230207194937.122543-3-willy@infradead.org/
>
> It survives a run of xfstests. If your architecture doesn't store its
> PFNs at PAGE_SHIFT, you're going to want to implement your own set_ptes(),

riscv stores its pfn at PAGE_PFN_SHIFT instead of PAGE_SHIFT, se we need
to reimplement set_ptes. But I have been playing with your patchset and
we never fall into the case where set_ptes is called with nr > 1, any
idea why? I booted a large ubuntu defconfig and launched
will_it_scale.page_fault4.

I'll come up with the proper implementation of set_ptes anyway soon.

Thanks,

Alex

> or you'll see entirely the wrong pages mapped into userspace. You may
> also wish to implement set_ptes() if it can be done more efficiently
> than __pte(pteval(pte) + PAGE_SIZE).
>
> Architectures that implement things like flush_icache_page() and
> update_mmu_cache() may want to propose batched versions of those.
> That's alpha, csky, m68k, mips, nios2, parisc, sh,
> arm, loongarch, openrisc, powerpc, riscv, sparc and xtensa.
> Maintainers BCC'd, mailing lists CC'd.
>
> I'm happy to collect implementations and submit them as part of a v6.
>
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