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Mon, 1 Mar 2021 12:59:24 +0000 (UTC) Subject: Re: [PATCH v3 0/2] Make alloc_contig_range handle Hugetlb pages To: Oscar Salvador Cc: Andrew Morton , Mike Kravetz , Muchun Song , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210222135137.25717-1-osalvador@suse.de> <20210301125754.GA4003@linux> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <8c230cb6-9c29-eaec-c548-46199611b1e6@redhat.com> Date: Mon, 1 Mar 2021 13:59:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210301125754.GA4003@linux> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 559B1DE X-Stat-Signature: z7nbhgm5xuakwm1gabefpqf1asgh61nw Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf04; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614603569-684630 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 01.03.21 13:57, Oscar Salvador wrote: > On Mon, Mar 01, 2021 at 01:43:00PM +0100, David Hildenbrand wrote: >> Same experiment with ZONE_MOVABLE: >> >> a) Free huge pages: all memory can get unplugged again. >> >> b) Allocated/populated but idle huge pages: all memory can get unplugged >> again. >> >> c) Allocated/populated but all 512 huge pages are read/written in a loop: >> all memory can get unplugged again, but I get a single >> >> [ 121.192345] alloc_contig_range: [180000, 188000) PFNs busy >> >> Most probably because it happened to try migrating a huge page while it was >> busy. As virtio-mem retries on ZONE_MOVABLE a couple of times, it can deal >> with this temporary failure. >> >> >> >> Last but not least, I did something extreme: >> >> ]# cat /proc/meminfo >> MemTotal: 5061568 kB >> MemFree: 186560 kB >> MemAvailable: 354524 kB >> ... >> HugePages_Total: 2048 >> HugePages_Free: 2048 >> HugePages_Rsvd: 0 >> HugePages_Surp: 0 >> >> >> Triggering unplug would require to dissolve+alloc - which now fails when >> trying to allocate an additional ~512 huge pages (1G). >> >> >> As expected, I can properly see memory unplug not fully succeeding. + I get >> a fairly continuous stream of >> >> [ 226.611584] alloc_contig_range: [19f400, 19f800) PFNs busy >> ... >> >> But more importantly, the hugepage count remains stable, as configured by >> the admin (me): >> >> HugePages_Total: 2048 >> HugePages_Free: 2048 >> HugePages_Rsvd: 0 >> HugePages_Surp: 0 > > Thanks for giving it a spin David, that is highly appreciated ;-)! > > I will add above information in next's version changelog if you do not mind, > so the before-and-after can be seen clearly. > > I shall send v4 in the course of the next few days. > I'll have some review feedback on error handling that might be improved, I'll share that shortly. -- Thanks, David / dhildenb