Re: API for setting multiple PTEs at once

From: "Yin, Fengwei" <fengwei.yin@intel.com>
To: Alexandre Ghiti <alex@ghiti.fr>,
	Matthew Wilcox <willy@infradead.org>,
	<linux-arch@vger.kernel.org>
Cc: <linux-mm@kvack.org>, <linux-alpha@vger.kernel.org>,
	<linux-csky@vger.kernel.org>, <linux-m68k@lists.linux-m68k.org>,
	<linux-mips@vger.kernel.org>, Dinh Nguyen <dinguyen@kernel.org>,
	<linux-parisc@vger.kernel.org>, <linux-sh@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<loongarch@lists.linux.dev>, <openrisc@lists.librecores.org>,
	<linuxppc-dev@lists.ozlabs.org>,
	<linux-riscv@lists.infradead.org>, <sparclinux@vger.kernel.org>,
	<linux-xtensa@linux-xtensa.org>
Subject: Re: API for setting multiple PTEs at once
Date: Wed, 8 Feb 2023 20:09:00 +0800	[thread overview]
Message-ID: <b44d5dc7-ee7a-80e0-5401-829bf5740de5@intel.com> (raw)
In-Reply-To: <ba99ed28-61e4-4acd-ce17-338f5a49ef26@ghiti.fr>


On 2/8/2023 7:23 PM, Alexandre Ghiti wrote:
> 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.
Need to use xfs filesystem to get large folio for file mapping.
Other filesystem may be also OK. But I just tried xfs. Thanks.


Regards
Yin, Fengwei

> 
> 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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