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Mon, 22 May 2023 11:47:51 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <0471c62b-7047-050a-14f5-f47dfaffaba7@I-love.SAKURA.ne.jp> Date: Mon, 22 May 2023 11:47:25 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH] lib/stackdepot: stackdepot: don't use __GFP_KSWAPD_RECLAIM from __stack_depot_save() if atomic context To: "Huang, Ying" Cc: syzbot , syzkaller-bugs@googlegroups.com, Mel Gorman , Vlastimil Babka , Andrew Morton , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Andrey Ryabinin , kasan-dev , linux-mm , Johannes Weiner , Michal Hocko References: <000000000000cef3a005fc1bcc80@google.com> <48a6a627-183d-6331-0d8d-ae4b1d4b0101@I-love.SAKURA.ne.jp> <9c44eba9-5979-ee78-c9c8-626edc00f975@I-love.SAKURA.ne.jp> <87edn92jvz.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Language: en-US From: Tetsuo Handa In-Reply-To: <87edn92jvz.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0C8B180002 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: f347mtyzwp3c4hjz6ezr5oi1jxmhhhwk X-HE-Tag: 1684723702-275100 X-HE-Meta: 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 /L6UwikH u9Klk8BpRx5m4w/VVmbfcHoE7Jxklo3u3SVB8E7Nn4egA7ip+Sjf9/TV0BAALGU6eE9dSu/6+JRwSRrcfC5kWl0LuoUA4BTVXNUlZQdAwzZy7Qq1tSPgVAg+YGJAZJ4ZIVYR21W9sqGXDNus4TL1en+sl0UUkv3XbFzsc77KuawKcfFW6JV+4k9NkVvhgbBt+Rc/G/WYLjd5X4ZpSMkI/B8OdITaR2kwMEg9HeGevo9LqyIIXsZrJ1ctigDLN15eCzXxRMaBN01y6SMSZRtAL74xnFYdnvyROUfwBZziGE3eByqNcpRjp11CCPmYEjOz8Fr92hfNrsCvwtOrQdxywlkmU21uOGGtLWYcuIrLFCFehnk4= 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: On 2023/05/22 11:13, Huang, Ying wrote: >> Any atomic allocation used by KASAN needs to drop __GFP_KSWAPD_RECLAIM bit. >> Where do we want to drop this bit (in the caller side, or in the callee side)? > > Yes. I think we should fix the KASAN. Maybe define a new GFP_XXX > (instead of GFP_ATOMIC) for debug code? The debug code may be called at > almost arbitrary places, and wakeup_kswap() isn't safe to be called in > some situations. What do you think about removing __GFP_KSWAPD_RECLAIM from GFP_ATOMIC and GFP_NOWAIT? Recent reports indicate that atomic allocations (GFP_ATOMIC and GFP_NOWAIT) are not safe enough to think "atomic". They just don't do direct reclaim, but they do take spinlocks. Removing __GFP_KSWAPD_RECLAIM from GFP_ATOMIC and GFP_NOWAIT simplifies locking dependency and reduces latency of atomic allocations (which is important when called from "atomic" context). I consider that memory allocations which do not do direct reclaim should be geared towards less locking dependency. In general, GFP_ATOMIC or GFP_NOWAIT users will not allocate many pages. It is likely that somebody else tries to allocate memory using __GFP_DIRECT_RECLAIM right after GFP_ATOMIC or GFP_NOWAIT allocations. We unlikely need to wake kswapd upon GFP_ATOMIC or GFP_NOWAIT allocations. If some GFP_ATOMIC or GFP_NOWAIT users need to allocate many pages, they can add __GFP_KSWAPD_RECLAIM explicitly; though allocating many pages using GFP_ATOMIC or GFP_NOWAIT is not recommended from the beginning...