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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] mm/page_alloc: replace local_lock with normal spinlock -fix -fix Content-Language: en-US To: Mel Gorman , Andrew Morton Cc: Nicolas Saenz Julienne , Marcelo Tosatti , Michal Hocko , Hugh Dickins , Yu Zhao , Marek Szyprowski , LKML , Linux-MM References: <20220708144406.GJ27531@techsingularity.net> From: Vlastimil Babka In-Reply-To: <20220708144406.GJ27531@techsingularity.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657292090; 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=l7Aw7CUlH7hnP8Qg6TBNYPcNryVs2jtH5tretlprBAE=; b=ZBHsQhHclBfi7g7DuVBkRUP57iuwdRIUo+nqQZ0/nHMkUUtIW1OvsUOlrEH987/QAGB/71 xFwLelJSixk352SiP/9j5JEzvEd4Ook50RmQmqWBkSZG6GPU+t8iNKHdObE+eRRyU1s194 HLzvYGeP/Y0hu6xxRCyszRUb7qxTKtk= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657292090; a=rsa-sha256; cv=none; b=XG6OpBzXvGYiLfjLLgQz3jBu2wAJOugqDet1L/aeYPRMheC//KAum0bAI3hk/JBLyDlbYF 7OvtNPJabymrXtSKMzXFfLZH9FIjknU+Q4/Ha5miErhojRsUkGdcZjyqCW0br/MYSmX/Jx gmAI3DghPT+tjFwtILj7OQwVZ1rCYAU= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=ecouykwp; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=108E4Ct+; dmarc=none; spf=pass (imf30.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=ecouykwp; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=108E4Ct+; dmarc=none; spf=pass (imf30.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Stat-Signature: 6f7d45ffkird6ttbmoq6tde9pg46f3os X-Rspamd-Queue-Id: CCDF08005F X-Rspamd-Server: rspam07 X-Rspam-User: X-HE-Tag: 1657292089-736267 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 7/8/22 16:44, Mel Gorman wrote: > pcpu_spin_unlock and pcpu_spin_unlock_irqrestore both unlock > pcp->lock and then enable preemption. This lacks symmetry against > both the pcpu_spin helpers and differs from how local_unlock_* is > implemented. While this is harmless, it's unnecessary and it's generally > better to unwind locks and preemption state in the reverse order as > they were acquired. Hm I'm confused, it seems it's done in reverse order (which I agree with) before this -fix-fix, but not after it? before, pcpu_spin_lock() (and variants) do pcpu_task_pin() and then spin_lock() (or variant), and pcpu_spin_unlock() does spin_unlock() and then pcpu_task_unpin(). That seems symmetrical, i.e. reverse order to me? And seems to match what local_lock family does too. > This is a fix on top of the mm-unstable patch > mm-page_alloc-replace-local_lock-with-normal-spinlock-fix.patch > > Signed-off-by: Mel Gorman > --- > mm/page_alloc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 934d1b5a5449..d0141e51e613 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -192,14 +192,14 @@ static DEFINE_MUTEX(pcp_batch_high_lock); > > #define pcpu_spin_unlock(member, ptr) \ > ({ \ > - spin_unlock(&ptr->member); \ > pcpu_task_unpin(); \ > + spin_unlock(&ptr->member); \ > }) > > #define pcpu_spin_unlock_irqrestore(member, ptr, flags) \ > ({ \ > - spin_unlock_irqrestore(&ptr->member, flags); \ > pcpu_task_unpin(); \ > + spin_unlock_irqrestore(&ptr->member, flags); \ > }) > > /* struct per_cpu_pages specific helpers. */