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Tue, 14 Apr 2020 15:55:07 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 30bqm261nh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 14 Apr 2020 15:55:06 +0000 Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 03EFt5na015079; Tue, 14 Apr 2020 15:55:05 GMT Received: from ca-dmjordan1.us.oracle.com (/10.211.9.48) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 14 Apr 2020 08:55:05 -0700 Date: Tue, 14 Apr 2020 11:55:25 -0400 From: Daniel Jordan To: Chintan Pandya Cc: Alexander Duyck , Prathu Baronia , Andrew Morton , linux-mm , Greg KH , "gthelen@google.com" , "jack@suse.cz" , Michal Hocko , Ken Lin , Gasine Xu Subject: Re: [RFC] mm/memory.c: Optimizing THP zeroing routine for !HIGHMEM cases Message-ID: <20200414155525.6s5wlsdiktocs3c3@ca-dmjordan1.us.oracle.com> References: <20200403081812.GA14090@oneplus.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9591 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 mlxlogscore=805 adultscore=0 mlxscore=0 phishscore=0 malwarescore=0 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004140125 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9591 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 adultscore=0 mlxlogscore=847 clxscore=1011 mlxscore=0 phishscore=0 suspectscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 priorityscore=1501 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004140125 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 Sat, Apr 11, 2020 at 08:45:35AM +0000, Chintan Pandya wrote: > > > +#else > > > +void clear_huge_page(struct page *page, > > > + unsigned long addr_hint, unsigned int > > > +pages_per_huge_page) { > > > + void *addr; > > > + > > > + addr = page_address(page); > > > + memset(addr, 0, pages_per_huge_page*PAGE_SIZE); } #endif > > > > This seems like a very simplistic solution to the problem, and I am worried > > something like this would introduce latency issues when pages_per_huge_page > > gets to be large. It might make more sense to just wrap the process_huge_page > > call in the original clear_huge_page and then add this code block as an #else > > case. That way you avoid potentially stalling a system for extended periods of > > time if you start trying to clear 1G pages with the function. > > > > One interesting data point would be to see what the cost is for breaking this up > > into a loop where you only process some fixed number of pages and running it > > with cond_resched() so you can avoid introducing latency spikes. > > As per the patch above, it's not using kmap_atomic() and hence preemption & page_fault > are not disabled. Do we still need to explicitly call cond_resched() in this case? > #justAsking Didn't see this answered on the list, but the answer is yes because the kernel may not have CONFIG_PREEMPTION enabled.