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 E0BD8C25B74 for ; Mon, 27 May 2024 18:49:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 43A846B0082; Mon, 27 May 2024 14:49:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3E9466B0085; Mon, 27 May 2024 14:49:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2B1206B0088; Mon, 27 May 2024 14:49:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 0B7F96B0082 for ; Mon, 27 May 2024 14:49:39 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id BCCD44139B for ; Mon, 27 May 2024 18:49:38 +0000 (UTC) X-FDA: 82165064436.21.8EECD9B Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf23.hostedemail.com (Postfix) with ESMTP id AE96F140010 for ; Mon, 27 May 2024 18:49:36 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="G7/JoEQ5"; spf=pass (imf23.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1716835776; 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=er9zpPdeV49PUDKJxQuU67Pcm6GfUTc6DyJ/Kh2n3Ps=; b=6bZjQYnRJg8MygRTYVUxwGorybxYpTJ3seGJyrCyxRa6gmPUypR6iHbl/8//p0eZENot+i 4O8zoG7FxQRKMkPwCkcndWoWfgc9XBWuNHQuoy6OwZujOGuW+ziUu+ePut7UCOU3zQXgOQ aiGaTpDi8flSjRKxhGOe9NoZHtKVDAs= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1716835776; a=rsa-sha256; cv=none; b=t/u/J4+tGaAD0RIFm/8Nf2MKGF5GaBGM9JgFM0fGYs/3Tjq1VyhAOJHk9Ahaa+dq4mjSzN wJxMn2hRoo2xUGlE12uC+zj3BcjM/ZCOhf6Pv+EkBNqk7L8y+l6uDiDw0/nQGpssM6r4S8 HNniTjPsPVgCW7gMgaAgRRTAA7gNl5I= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="G7/JoEQ5"; spf=pass (imf23.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1716835775; 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; bh=er9zpPdeV49PUDKJxQuU67Pcm6GfUTc6DyJ/Kh2n3Ps=; b=G7/JoEQ5+jUKPBKMODtil4tOkfsJp/IipfbCy2tSYcPReln0PaN5y98659OGDzP5FYga14 SeF0+mCFG6a0Up3p1HAn1ZMD4828OC5mD9AZanLR0bZOQh0CddQV8Z6D40+FSlclELBDgh /DqJBfM/3ATktGq94oHJiwmTWZT1p64= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-171-vXd5DfyRP_SfK4Bv8nPiYA-1; Mon, 27 May 2024 14:49:32 -0400 X-MC-Unique: vXd5DfyRP_SfK4Bv8nPiYA-1 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-354fb2cf5b0so28063f8f.1 for ; Mon, 27 May 2024 11:49:32 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1716835771; x=1717440571; h=content-transfer-encoding:in-reply-to:content-language:from :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=er9zpPdeV49PUDKJxQuU67Pcm6GfUTc6DyJ/Kh2n3Ps=; b=KmZktDxGOdQQRcAxeF9wJXvjTJwm8q0YIOUBLMunjyfdc2bkzqcql+PR4auyjgD83q ByAbkd2t3hTnZptd5Yk2ktF87VcOivhf81M5MHFkhNmnK6l81luK0eb/hMGPJchwSQjh LmToJP9Af9K/M5HGAcut/izIKBd8gqETEGpbdM+qKcEvFIif0bfeKiXjLI3Z4CEATc3C jZ+c3X4ICsdiS/QG6flZNOElcA/AnApuDWtXBs6Asy8MAVCNJInL9smi99EHxIUz8+qI Isf0g7jxw5aWa/ntT+ddwyfpdXjUyfwS0SssyKEPY7gRN14Vj78QzzNozpbWf5V8jvgz kBjQ== X-Forwarded-Encrypted: i=1; AJvYcCWtJhVKX3lG69tE5Ab43Ba7UMEltvipbVK3t6mYI5JWYEx8F634Grc5hML3a2Rt1CJtdgn+VoQT7s7Y4316M/uOjyc= X-Gm-Message-State: AOJu0YyQZIjDugwQYD+ZWNfbZGksHqMmF+FFL2Bp7g5POF/Q7Qt2x3WH y4KocllysGFWAvnZm3OImizh/6jvnS7LiBt7HuUQLkuSbgej7Vh9Ex4wK9MJxZgzDWUWoCQESpE DGnTx3OIgkkykseyzr2W6XzNgv+5DbKg47KhObi+/WWTIdFyP X-Received: by 2002:a5d:498a:0:b0:354:f57f:7bdd with SMTP id ffacd0b85a97d-3552fe0292fmr6791888f8f.45.1716835771335; Mon, 27 May 2024 11:49:31 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFnQ45GrmOD8w4iBJnqvAdq3EeerBIwdqkHXyVUjWg4x+oSG0Q4szUswefeawEbDqXjYy0Dsw== X-Received: by 2002:a5d:498a:0:b0:354:f57f:7bdd with SMTP id ffacd0b85a97d-3552fe0292fmr6791871f8f.45.1716835770904; Mon, 27 May 2024 11:49:30 -0700 (PDT) Received: from ?IPV6:2003:d8:2f28:4600:d3a7:6c26:54cf:e01e? (p200300d82f284600d3a76c2654cfe01e.dip0.t-ipconnect.de. [2003:d8:2f28:4600:d3a7:6c26:54cf:e01e]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a626c817c81sm516319366b.28.2024.05.27.11.49.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 May 2024 11:49:30 -0700 (PDT) Message-ID: <00ba1dff-7c05-46e8-b0d9-a78ac1cfc198@redhat.com> Date: Mon, 27 May 2024 20:49:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/6] mm: allow reuse of the lower 16 bit of the page type with an actual type To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Mike Rapoport , Minchan Kim , Sergey Senozhatsky , Hyeonggon Yoo <42.hyeyoo@gmail.com> References: <20240527141454.113132-1-david@redhat.com> <20240527141454.113132-3-david@redhat.com> From: David Hildenbrand 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: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: AE96F140010 X-Rspam-User: X-Stat-Signature: ysmb1c4nrt5as6kp4nzybnmsm431mpzb X-HE-Tag: 1716835776-714027 X-HE-Meta: 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 +TKitRyh 7dcKQowLCyQouYNb9og2jTflHVdFRlBtvmwVa6L225ZuF7BMy4RZdMW/+gOlEmYHRdVgtvRaaP3izEuH6+wDt2/rkSb/kJ5sW/w1O6sXIklyl3lM= 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: Am 27.05.24 um 17:26 schrieb Matthew Wilcox: > On Mon, May 27, 2024 at 04:14:50PM +0200, David Hildenbrand wrote: >> As long as the owner sets a page type first, we can allow reuse of the >> lower 18 bit: sufficient to store an offset into a 64 KiB page, which > > You say 18 here and 16 below. Thanks, missed to fixup one instance after going back and forth. > >> is the maximum base page size in *common* configurations (ignoring the >> 256 KiB variant). Restrict it to the head page. >> >> We'll use that for zsmalloc next, to set a proper type while still >> reusing that field to store information (offset into a base page) that >> cannot go elsewhere for now. >> >> Fear of running out of bits for storing the actual type? Actually, we >> don't need one bit per type, we could store a single value instead. >> Further, we could likely limit PAGE_TYPE_BASE to a single (highest) bit. > > We could, but it's more instructions to check. Maybe, and maybe not sufficient more that we care. I was thinking of something like the following (probably broken but you should get the idea): /* * If the _mapcount is negative, we might store a page type. The * page_type field corresponds to the most significant byte of the * _mapcount field. As the mapcount is initialized to -1, we have no * type as defaults. We have plenty of room to underflow the mapcount * before we would end up indicating a valid page_type. */ #define PAGE_TYPE_BASE 0x80 enum page_type { PT_buddy = PAGE_TYPE_BASE, PT_offline, PT_table, PT_guard, PT_hugetlb, PT_slab, /* we must forbid page_type == -1 */ PT_unusable = 0xff }; In struct page: union { atomic_t _mapcount; #if __BYTE_ORDER == __BIG_ENDIAN struct { uint16_t page_type_data; uint8_t page_type_reserved; uint8_t page_type; }; #else struct { uint8_t page_type; uint8_t page_type_reserved; uint16_t page_type_data; }; #end }; #define PageType(page, type) (page->page_type == type) Once could maybe also change page_has_type to simply work on the fact that the highest bit must be set and any other bit of the type must be clear: static inline int page_has_type(const struct page *page) { return (page->page_type & PAGE_TYPE_BASE) && page->page_type != 0xffff; } But just some thought. > >> +++ b/include/linux/page-flags.h >> @@ -945,14 +945,18 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) >> */ >> >> #define PAGE_TYPE_BASE 0xf0000000 >> -/* Reserve 0x0000007f to catch underflows of _mapcount */ >> -#define PAGE_MAPCOUNT_RESERVE -128 >> -#define PG_buddy 0x00000080 >> -#define PG_offline 0x00000100 >> -#define PG_table 0x00000200 >> -#define PG_guard 0x00000400 >> -#define PG_hugetlb 0x00000800 >> -#define PG_slab 0x00001000 >> +/* >> + * Reserve 0x0000ffff to catch underflows of _mapcount and >> + * allow owners that set a type to reuse the lower 16 bit for their own >> + * purposes. >> + */ >> +#define PAGE_MAPCOUNT_RESERVE -65536 > > I think my original comment was misleading. This should be: > > * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflow. Makes sense. > > How about we start at the top end and let people extend down? ie: > > #define PAGE_TYPE_BASE 0x80000000 > #define PG_buddy 0x40000000 > #define PG_offline 0x20000000 > #define PG_table 0x10000000 > #define PG_guard 0x08000000 > #define PG_hugetlb 0x04000000 > #define PG_slab 0x02000000 > #define PAGE_MAPCOUNT_RESERVE (~0x0000ffff) > > Now we can see that we have 9 flags remaining, which should last until > we can have proper memdesc typing. Also works for me. Thanks! -- Thanks, David / dhildenb