linux-kernel - Re: [PATCH v6 18/18] arm64/mm: Automatically fold contpte mappings

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Message-ID: <306874fe-9bc1-4dec-a856-0125e4541971@arm.com>
Date: Tue, 25 Jun 2024 13:41:02 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>,
 James Morse <james.morse@....com>, Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Mark Rutland <mark.rutland@....com>,
 David Hildenbrand <david@...hat.com>, John Hubbard <jhubbard@...dia.com>,
 Zi Yan <ziy@...dia.com>, Barry Song <21cnbao@...il.com>,
 Alistair Popple <apopple@...dia.com>, Yang Shi <shy828301@...il.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Yin, Fengwei" <fengwei.yin@...el.com>
Cc: linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 18/18] arm64/mm: Automatically fold contpte mappings

On 25/06/2024 13:37, Baolin Wang wrote:

[...]

>>> For other filesystems, like ext4, I did not found the logic to determin what
>>> size of folio to allocate in writable mmap() path
>>
>> Yes I'd be keen to understand this to. When I was doing contpte, page cache
>> would only allocate large folios for readahead. So that's why I wouldn't have
> 
> You mean non-large folios, right?

No I mean that at the time I wrote contpte, the policy was to allocate an
order-0 folio for any writes that missed in the page cache, and allocate large
folios only when doing readahead from storage into page cache. The test that is
regressing is doing writes.