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X-IronPort-AV: E=McAfee;i="6600,9927,10712"; a="349125523" X-IronPort-AV: E=Sophos;i="5.99,280,1677571200"; d="scan'208";a="349125523" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 May 2023 17:24:53 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10712"; a="732181480" X-IronPort-AV: E=Sophos;i="5.99,280,1677571200"; d="scan'208";a="732181480" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 May 2023 17:24:50 -0700 From: "Huang, Ying" To: David Hildenbrand Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Johannes Weiner , Matthew Wilcox , Michal Hocko , Minchan Kim , Tim Chen , Yang Shi , Yu Zhao Subject: Re: [PATCH] swap: cleanup get/put_swap_device usage References: <20230516052957.175432-1-ying.huang@intel.com> Date: Wed, 17 May 2023 08:23:18 +0800 In-Reply-To: (David Hildenbrand's message of "Tue, 16 May 2023 13:06:03 +0200") Message-ID: <87fs7v7qmh.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Queue-Id: 3ACE140010 X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: kuqqd8mpwr33a7j194t6d68h5fy563i5 X-HE-Tag: 1684283094-101520 X-HE-Meta: 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 Raa0dUS2 MkDmqF9EBHLBk7FMppQQtlm41/08TYGE/pJSO4pK8WO6nsIu0VEjAZQXsq1p64qawSerBzBI4al+1cmoahTbDx0u/WoU7ZKmErHmr6TyyWfO0EClM8h2SVARve3G5jsVuoKKXHYKNpnyj53pHEiXhBAoqk26qExJ/fkZ5vOZb57uhcGEV99Z4h6/U227nsmx+iyot+WVPDbPLyQdxbO5k7MXjJw== 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: David Hildenbrand writes: > On 16.05.23 07:29, Huang Ying wrote: >> The general rule to use a swap entry is as follows. >> When we get a swap entry, if there isn't some other way to prevent >> swapoff, such as page lock for swap cache, page table lock, etc., the >> swap entry may become invalid because of swapoff. Then, we need to >> enclose all swap related functions with get_swap_device() and >> put_swap_device(), unless the swap functions call >> get/put_swap_device() by themselves. >> Add the rule as comments of get_swap_device(), and cleanup some >> functions which call get/put_swap_device(). >> 1. Enlarge the get/put_swap_device() protection range in >> __read_swap_cache_async(). This makes the function a little easier to >> be understood because we don't need to consider swapoff. And this >> makes it possible to remove get/put_swap_device() calling in some >> function called by __read_swap_cache_async(). >> 2. Remove get/put_swap_device() in __swap_count(). Which is call in >> do_swap_page() only, which encloses the call with get/put_swap_device() >> already. >> 3. Remove get/put_swap_device() in __swp_swapcount(). Which is call >> in __read_swap_cache_async() only, which encloses the call with >> get/put_swap_device() already. >> 4. Remove get/put_swap_device() in __swap_duplicate(). Which is >> called >> by >> - swap_shmem_alloc(): the swap cache is locked. >> - copy_nonpresent_pte() -> swap_duplicate() and try_to_unmap_one() >> -> >> swap_duplicate(): the page table lock is held. >> - __read_swap_cache_async() -> swapcache_prepare(): enclosed with >> get/put_swap_device() already. >> Other get/put_swap_device() usages are checked too. > > I suggest splitting this patch up into logical pieces as outlined here > by you already. OK. Will do that in the next version. Best Regards, Huang, Ying