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Received: from foss.arm.com ([217.140.110.172]) by desiato.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1uFE55-0000000HEga-1vXk for linux-arm-kernel@lists.infradead.org; Wed, 14 May 2025 15:31:41 +0000 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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250514_163139_888713_0B6CE3BD X-CRM114-Status: GOOD ( 18.29 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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