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imf08.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf08.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1747236697; a=rsa-sha256; cv=none; b=psdLW7WZlQtk4/PGSuMpG1j70hJeF7lOJmrhCH88ylhv0MpF8dXMakMOawaQdkWArSyZqR DlNXXvs0lc/kcc2LMp1DXm58ZGBbuW8a0R1bVfKMO6I89tKVtH4wy5aJObXJI6UpOrmoqG A/UarSwDexSkk8rY6b0qqepydQjvU9g= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D8782150C; Wed, 14 May 2025 08:31:24 -0700 (PDT) Received: from [10.57.91.10] (unknown [10.57.91.10]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8A34F3F5A1; Wed, 14 May 2025 08:31:33 -0700 (PDT) Message-ID: <933f4191-4075-4b02-998a-35b1711e778c@arm.com> Date: Wed, 14 May 2025 16:31:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 5/5] mm/filemap: Allow arch to request folio size for exec memory Content-Language: en-GB To: Will Deacon Cc: Andrew Morton , "Matthew Wilcox (Oracle)" , Alexander Viro , Christian Brauner , Jan Kara , David Hildenbrand , Dave Chinner , Catalin Marinas , Kalesh Singh , Zi Yan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20250430145920.3748738-1-ryan.roberts@arm.com> <20250430145920.3748738-6-ryan.roberts@arm.com> <20250509135223.GB5707@willie-the-truck> <20250514151400.GB10762@willie-the-truck> From: Ryan Roberts In-Reply-To: <20250514151400.GB10762@willie-the-truck> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 13892160011 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 7st19d5j7hkk6d3opqom4wizxdd1pa7w X-HE-Tag: 1747236696-431762 X-HE-Meta: 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 y3E3d3v4 +gapeT4mLCb5MR4HykU7JeSdXO3MVbXPuplVkS+75wpTKrlCP4lHG+nCsBtV4BoKAwhIPKA30ZaRbIwhADPSSQqWMoL1DDY1wo8uXroS/xdB8h1qETToDHrpqsBMWmvb1eLmHl9tuoPdiHKjs3/OwumI++w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 14/05/2025 16:14, Will Deacon wrote: > On Tue, May 13, 2025 at 01:46:06PM +0100, Ryan Roberts wrote: >> On 09/05/2025 14:52, Will Deacon wrote: >>> On Wed, Apr 30, 2025 at 03:59:18PM +0100, Ryan Roberts wrote: >>>> diff --git a/mm/filemap.c b/mm/filemap.c >>>> index e61f374068d4..37fe4a55c00d 100644 >>>> --- a/mm/filemap.c >>>> +++ b/mm/filemap.c >>>> @@ -3252,14 +3252,40 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) >>>> if (mmap_miss > MMAP_LOTSAMISS) >>>> return fpin; >>>> >>>> - /* >>>> - * mmap read-around >>>> - */ >>>> fpin = maybe_unlock_mmap_for_io(vmf, fpin); >>>> - ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2); >>>> - ra->size = ra->ra_pages; >>>> - ra->async_size = ra->ra_pages / 4; >>>> - ra->order = 0; >>>> + if (vm_flags & VM_EXEC) { >>>> + /* >>>> + * Allow arch to request a preferred minimum folio order for >>>> + * executable memory. This can often be beneficial to >>>> + * performance if (e.g.) arm64 can contpte-map the folio. >>>> + * Executable memory rarely benefits from readahead, due to its >>>> + * random access nature, so set async_size to 0. >>> >>> In light of this observation (about randomness of instruction fetch), do >>> you think it's worth ignoring VM_RAND_READ for VM_EXEC? >> >> Hmm, yeah that makes sense. Something like: >> >> ---8<--- >> diff --git a/mm/filemap.c b/mm/filemap.c >> index 7b90cbeb4a1a..6c8bf5116c54 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -3233,7 +3233,8 @@ static struct file *do_sync_mmap_readahead(struct vm_fault >> *vmf) >> if (!ra->ra_pages) >> return fpin; >> >> - if (vm_flags & VM_SEQ_READ) { >> + /* VM_EXEC case below is already intended for random access */ >> + if ((vm_flags & (VM_SEQ_READ | VM_EXEC)) == VM_SEQ_READ) { >> fpin = maybe_unlock_mmap_for_io(vmf, fpin); >> page_cache_sync_ra(&ractl, ra->ra_pages); >> return fpin; >> ---8<--- > > I was thinking about the: > > if (vm_flags & VM_RAND_READ) > return fpin; Yes sorry, I lost my mind when doing that patch... I intended to do it for the VM_RAND_READ as you suggested, but my fingers did something completely different. > > code above this which bails if VM_RAND_READ is set. That seems contrary > to the code you're adding which says that, even for random access > patterns where readahead doesn't help, it's still worth sizing the folio > appropriately for contpte mappings. Anyway, I totally agree with this. So I'll avoid the early return VM_RAND_READ if VM_EXEC is also set. Thanks, Ryan > > Will