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bh=632v7CpS3QPt9HhoeHrpEHCN5Oo6OBT/aBsHaC13wJY=; b=4RWwypsh/b1DxIEgQSwJa7inry57ujp0PresSVkMyspBaFU1HX4PromBZGoY9YKqR7TVwD H37uGAU5gQMHgDv3T9gb132AhFZ5dEW+I+r9Tm9zQ5WUhCK6qn7zGiA0Ba94xqyOIaMLB0 0od4tH93Zi6Agm7bGSoscoq2yx4A5KMdc2O7nNuNHkVK62RERbDb8jbatYYn6I5v0E6UjJ l8fgMsKn0PP0fSSzUj6rApDjBqkAlNvmG2sQmZ16MnwIliklQyl8DJPRfMj6qR9zPNiK+J 7vQWH/jPkxGKQlY7dluCf3BocQcXJhKNmTBq9ROA+69L7nUISTrtM3I67geuAg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1740662381; 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: in-reply-to:in-reply-to:references:references; bh=632v7CpS3QPt9HhoeHrpEHCN5Oo6OBT/aBsHaC13wJY=; b=63ZblLAFx8Q9BJMFP8YmpzPUbtp3qT/fznqsvToR8Xgeiv5Ra2TQxxIHHfuAaNuNSqCwuf AIblV8hsvxwf44Bw== From: Sebastian Andrzej Siewior To: Sergey Senozhatsky Cc: Andrew Morton , Yosry Ahmed , Hillf Danton , Kairui Song , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 14/17] zram: permit reclaim in zstd custom allocator Message-ID: <20250227131940.6yzjRQmL@linutronix.de> References: <20250221222958.2225035-1-senozhatsky@chromium.org> <20250221222958.2225035-15-senozhatsky@chromium.org> <20250224091036.Y9fHrKr-@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 428E61C0030 X-Rspamd-Server: rspam12 X-Stat-Signature: 66hkehw1b7dq73k7jqq5qegeqhxhstr1 X-HE-Tag: 1740662685-50865 X-HE-Meta: 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 wwEPbsat yihVhufPQigp75Nin85P+EB0zl7M6jFJFfbiWru/AVvri4Xbsh1zmn5x4TVAkP9tT8mDExRjvu2Adjs4tlxRSDshdyuEyzepW2oXOf69OlMCSPEWlh3Q4Rat7QtixqGDgNETzBxc2QymyM2RU2Ces/2NG7bPZNdkpWS17c3ExZPMs/HWizAVG1cszGYCy7K0bePYB 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 2025-02-25 13:42:55 [+0900], Sergey Senozhatsky wrote: > On (25/02/24 10:10), Sebastian Andrzej Siewior wrote: > > On 2025-02-22 07:25:45 [+0900], Sergey Senozhatsky wrote: > > > static void *zstd_custom_alloc(void *opaque, size_t size) > > > { > > > - if (!preemptible()) > > > + /* Technically this should not happen */ > > > + if (WARN_ON_ONCE(!preemptible())) > > > return kvzalloc(size, GFP_ATOMIC); > > > > This check works only on preemptible kernels. > > I'm not sure this is true. > > > If you run this on !PREEMPTIBLE kernels, preemptible() reports always 0 > > so that WARNING will always trigger there. > > I thought that preemptible() depends on PREEMPT_COUNT, not on > PREEMPTIBLE, because even on !PREEMPTIBLE preempt-count still > holds hard/soft irq counts, etc. Yes. The preempt count is always there to hold NMI/ HARDIRQ/ SOFTIRQ. However only on a preemptible (that is with PREEMPT_COUNT) kernel preempt_disable() does something. So on !PREEMPTIBLE kernel you don't see spin_lock() or preempt_disable() reflect in preempt_count. Unless you enable debugging which force this option into a non-preemptible kernel. > I ran CONFIG_PREEMPT_NONE=y zram-zstd tests and didn't see any > warnings. Sebastian