From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E62D8C4829B for ; Mon, 12 Feb 2024 11:06:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2B4216B0072; Mon, 12 Feb 2024 06:06:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 262DF6B007B; Mon, 12 Feb 2024 06:06:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0DC9C6B0080; Mon, 12 Feb 2024 06:06:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id EBC326B007B for ; Mon, 12 Feb 2024 06:06:07 -0500 (EST) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id BEC5F809C9 for ; Mon, 12 Feb 2024 11:06:07 +0000 (UTC) X-FDA: 81782872374.13.940642F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf18.hostedemail.com (Postfix) with ESMTP id 763ED1C0006 for ; Mon, 12 Feb 2024 11:06:05 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Q8fBrNG6; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf18.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1707735965; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=7FqoqAesIGcQo2dISuvlgJNiDoSjW2RZdVRhvlHXipo=; b=m8OtoAanxg7+HR6bH0YAODvcM8aWiormyYG/wR0CJC4/TQqJe2HJf2FTMsxrQqZ1fC+Ut/ e/LgcY148NEVPhxGRgQLIlguK6XQ6itfKr7yn3Nt3jLx6G3j+DHe+XwViGm7oQ8SoL165D NmeUIXUJa8HRktF/J4xZUVvmm68dRZs= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Q8fBrNG6; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf18.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1707735965; a=rsa-sha256; cv=none; b=ddUTCkgJv8crXJ/KKPJpvJYCDlbn2ovt0kCeGdOCM0wowEsVOn/FApTxF/ddAgbQsDy96H Bfiw/n18fWOxGo1pJA3U9W3YT1WSq0lwrOWcFP0WD2Nm3ZPTE9vt2bDHza7W3tWtN5yuFp UFfRrr302vi/cTC/ZKmtT761WfnrfI0= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707735964; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=7FqoqAesIGcQo2dISuvlgJNiDoSjW2RZdVRhvlHXipo=; b=Q8fBrNG6ZZNq6NzzKdmF6bwfLBN+FnTZrIpY7/R7lI80myirZWjGC+aRlYX4e5vinNaPlN yiyWeHRqv8QARz+nlYcFi9SLm9BQiTnOPj5zxdT87VhFf8DtYwYlZgdWljBzOQD/sIO4qU Qq8TQ9LnhFFiY+4hpm4WprDbq5ggUss= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-244-L0ZTwwljMlq9rf7BgCKHFA-1; Mon, 12 Feb 2024 06:06:03 -0500 X-MC-Unique: L0ZTwwljMlq9rf7BgCKHFA-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-410c65efe5bso5638975e9.1 for ; Mon, 12 Feb 2024 03:06:03 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707735962; x=1708340762; h=content-transfer-encoding:in-reply-to:organization:autocrypt :references:cc:to:from:content-language:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=7FqoqAesIGcQo2dISuvlgJNiDoSjW2RZdVRhvlHXipo=; b=V6U255yaicUv1O7gJas15zFxPbRrQmRRNR+45dpFLfrYuG62bLVBuLf4KexEkuk1CF IveYW0JozT8PrbUtS3qvhbIxkLFRd2VhCabc30BWBcfa0MTeZLVXlaKO5zQ3yP+fvCZN W0qvFtiRAcc9Opts7m+Qx0F6iCgaqSmUJky4CJ8Yy0tAofadeWNBF6vKkVZBojDEfFHK 9bNAzkMRG4QNdZxSkxrBifLCe2Bmwgg+ihjcYh5FybPwpsNW1PZ5XObGxDWRaJJTXHqH PoDSlssfwni4oV+COyb4Xa9PpKX2IOmUA/N41mY0BmmnLcddYXECyfMnr/tk18W3Rb9Q UQJg== X-Gm-Message-State: AOJu0YwQVGqqcsIhA0mx+NKd/NTmccywD0wrkVA4xIhndNQTRQ30GIEj sg5ntbAR+D0jD47XomdOl7bQE96k0Cti63ikhzbG1zm2ZndiD/ViS2zScPUafuLqavKfPfCuCnP ckhPJR1pHibaJHNl25I3b/f0VyHLTqtaw3mTi7vpEfOmpC9XV X-Received: by 2002:a05:600c:4f51:b0:40f:b164:a415 with SMTP id m17-20020a05600c4f5100b0040fb164a415mr4095895wmq.25.1707735962318; Mon, 12 Feb 2024 03:06:02 -0800 (PST) X-Google-Smtp-Source: AGHT+IEb3whbUDNAx+XiP6uqByXUY70xbuTJym3UumyKe/MA+jY3HBbtBWUPQh3CjaxoVhB4AEqTCg== X-Received: by 2002:a05:600c:4f51:b0:40f:b164:a415 with SMTP id m17-20020a05600c4f5100b0040fb164a415mr4095877wmq.25.1707735961864; Mon, 12 Feb 2024 03:06:01 -0800 (PST) X-Forwarded-Encrypted: i=1; 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 Received: from ?IPV6:2003:cb:c730:2200:7229:83b1:524e:283a? (p200300cbc7302200722983b1524e283a.dip0.t-ipconnect.de. [2003:cb:c730:2200:7229:83b1:524e:283a]) by smtp.gmail.com with ESMTPSA id r2-20020a056000014200b0033b4acb999dsm6436120wrx.98.2024.02.12.03.06.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Feb 2024 03:06:01 -0800 (PST) Message-ID: <66ca6c58-1983-494f-b920-140be736f1d8@redhat.com> Date: Mon, 12 Feb 2024 12:05:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 09/10] mm/mmu_gather: improve cond_resched() handling with large folios and expensive page freeing From: David Hildenbrand To: Ryan Roberts , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Catalin Marinas , Yin Fengwei , Michal Hocko , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Michael Ellerman , Christophe Leroy , "Naveen N. Rao" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Arnd Bergmann , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org References: <20240209221509.585251-1-david@redhat.com> <20240209221509.585251-10-david@redhat.com> <6c66f7ca-4b14-4bbb-bf06-e81b3481b03f@redhat.com> <590946ad-a538-4c99-947f-93455c2d96c6@arm.com> Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 763ED1C0006 X-Stat-Signature: j314yiba5ng3hxsuduuy9if5qwmffgj3 X-HE-Tag: 1707735965-803861 X-HE-Meta: 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 5GyVnBCY 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 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 12.02.24 11:56, David Hildenbrand wrote: > On 12.02.24 11:32, Ryan Roberts wrote: >> On 12/02/2024 10:11, David Hildenbrand wrote: >>> Hi Ryan, >>> >>>>> -static void tlb_batch_pages_flush(struct mmu_gather *tlb) >>>>> +static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch) >>>>>   { >>>>> -    struct mmu_gather_batch *batch; >>>>> - >>>>> -    for (batch = &tlb->local; batch && batch->nr; batch = batch->next) { >>>>> -        struct encoded_page **pages = batch->encoded_pages; >>>>> +    struct encoded_page **pages = batch->encoded_pages; >>>>> +    unsigned int nr, nr_pages; >>>>>   +    /* >>>>> +     * We might end up freeing a lot of pages. Reschedule on a regular >>>>> +     * basis to avoid soft lockups in configurations without full >>>>> +     * preemption enabled. The magic number of 512 folios seems to work. >>>>> +     */ >>>>> +    if (!page_poisoning_enabled_static() && !want_init_on_free()) { >>>> >>>> Is the performance win really worth 2 separate implementations keyed off this? >>>> It seems a bit fragile, in case any other operations get added to free which are >>>> proportional to size in future. Why not just always do the conservative version? >>> >>> I really don't want to iterate over all entries on the "sane" common case. We >>> already do that two times: >>> >>> a) free_pages_and_swap_cache() >>> >>> b) release_pages() >>> >>> Only the latter really is required, and I'm planning on removing the one in (a) >>> to move it into (b) as well. >>> >>> So I keep it separate to keep any unnecessary overhead to the setups that are >>> already terribly slow. >>> >>> No need to iterate a page full of entries if it can be easily avoided. >>> Especially, no need to degrade the common order-0 case. >> >> Yeah, I understand all that. But given this is all coming from an array, (so >> easy to prefetch?) and will presumably all fit in the cache for the common case, >> at least, so its hot for (a) and (b), does separating this out really make a >> measurable performance difference? If yes then absolutely this optimizaiton >> makes sense. But if not, I think its a bit questionable. > > I primarily added it because > > (a) we learned that each cycle counts during mmap() just like it does > during fork(). > > (b) Linus was similarly concerned about optimizing out another batching > walk in c47454823bd4 ("mm: mmu_gather: allow more than one batch of > delayed rmaps"): > > "it needs to walk that array of pages while still holding the page table > lock, and our mmu_gather infrastructure allows for batching quite a lot > of pages. We may have thousands on pages queued up for freeing, and we > wanted to walk only the last batch if we then added a dirty page to the > queue." > > So if it matters enough for reducing the time we hold the page table > lock, it surely adds "some" overhead in general. > > >> >> You're the boss though, so if your experience tells you this is neccessary, then >> I'm ok with that. > > I did not do any measurements myself, I just did that intuitively as > above. After all, it's all pretty straight forward (keeping the existing > logic, we need a new one either way) and not that much code. > > So unless there are strong opinions, I'd just leave the common case as > it was, and the odd case be special. I think we can just reduce the code duplication easily: diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index d175c0f1e2c8..99b3e9408aa0 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -91,18 +91,21 @@ void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma) } #endif -static void tlb_batch_pages_flush(struct mmu_gather *tlb) -{ - struct mmu_gather_batch *batch; +/* + * We might end up freeing a lot of pages. Reschedule on a regular + * basis to avoid soft lockups in configurations without full + * preemption enabled. The magic number of 512 folios seems to work. + */ +#define MAX_NR_FOLIOS_PER_FREE 512 - for (batch = &tlb->local; batch && batch->nr; batch = batch->next) { - struct encoded_page **pages = batch->encoded_pages; +static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch) +{ + struct encoded_page **pages = batch->encoded_pages; + unsigned int nr, nr_pages; - while (batch->nr) { - /* - * limit free batch count when PAGE_SIZE > 4K - */ - unsigned int nr = min(512U, batch->nr); + while (batch->nr) { + if (!page_poisoning_enabled_static() && !want_init_on_free()) { + nr = min(MAX_NR_FOLIOS_PER_FREE, batch->nr); /* * Make sure we cover page + nr_pages, and don't leave @@ -111,14 +114,39 @@ static void tlb_batch_pages_flush(struct mmu_gather *tlb) if (unlikely(encoded_page_flags(pages[nr - 1]) & ENCODED_PAGE_BIT_NR_PAGES_NEXT)) nr++; + } else { + /* + * With page poisoning and init_on_free, the time it + * takes to free memory grows proportionally with the + * actual memory size. Therefore, limit based on the + * actual memory size and not the number of involved + * folios. + */ + for (nr = 0, nr_pages = 0; + nr < batch->nr && nr_pages < MAX_NR_FOLIOS_PER_FREE; + nr++) { + if (unlikely(encoded_page_flags(pages[nr]) & + ENCODED_PAGE_BIT_NR_PAGES_NEXT)) + nr_pages += encoded_nr_pages(pages[++nr]); + else + nr_pages++; + } + } - free_pages_and_swap_cache(pages, nr); - pages += nr; - batch->nr -= nr; + free_pages_and_swap_cache(pages, nr); + pages += nr; + batch->nr -= nr; - cond_resched(); - } + cond_resched(); } +} + +static void tlb_batch_pages_flush(struct mmu_gather *tlb) +{ + struct mmu_gather_batch *batch; + + for (batch = &tlb->local; batch && batch->nr; batch = batch->next) + __tlb_batch_free_encoded_pages(batch); tlb->active = &tlb->local; } -- 2.43.0 -- Cheers, David / dhildenb