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Wed, 20 Mar 2024 10:05:19 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id cw/GA9+0+mWBYgAAD6G6ig (envelope-from ); Wed, 20 Mar 2024 10:05:19 +0000 Date: Wed, 20 Mar 2024 11:06:45 +0100 From: Oscar Salvador To: Baolin Wang Cc: akpm@linux-foundation.org, muchun.song@linux.dev, david@redhat.com, linmiaohe@huawei.com, naoya.horiguchi@nec.com, mhocko@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/3] mm: hugetlb: make the hugetlb migration strategy consistent Message-ID: References: <3519fcd41522817307a05b40fb551e2e17e68101.1709719720.git.baolin.wang@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3519fcd41522817307a05b40fb551e2e17e68101.1709719720.git.baolin.wang@linux.alibaba.com> X-Rspamd-Queue-Id: 83C022001E X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: qxmbbjrsnamqxyti65oa4po981iyiwua X-HE-Tag: 1710929121-154228 X-HE-Meta: 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 OC5N8D/G Vht4PP6hoeRnLi3ER4iOht2gaw38lGRATDfRkngoU61SB9ghwds74FYwLDZVMSEvUVkHtiubeLtBeem+IIEBovOu4HkhtjP3mb3IN/H8s8StfwQ9YjuAKXkBP8iQTMzt3YpKZw0ZWEB8OkISH15yMD6h9KtEhnF9L1xj9He1ILwFHlqJkqFUlT+yCwEV1DxQ9ayPLVnDa+nVyIIpVNrN3Ekldzn5X+oy2jJYbsYZwjzspsB2jJvMRRUROtvm2ws/MiI8JOhEirBrpetVwjhBjw2nqwENuADP6JL36 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 Wed, Mar 06, 2024 at 06:13:27PM +0800, Baolin Wang wrote: > As discussed in previous thread [1], there is an inconsistency when handing > hugetlb migration. When handling the migration of freed hugetlb, it prevents > fallback to other NUMA nodes in alloc_and_dissolve_hugetlb_folio(). However, > when dealing with in-use hugetlb, it allows fallback to other NUMA nodes in > alloc_hugetlb_folio_nodemask(), which can break the per-node hugetlb pool > and might result in unexpected failures when node bound workloads doesn't get > what is asssumed available. > > To make hugetlb migration strategy more clear, we should list all the scenarios > of hugetlb migration and analyze whether allocation fallback is permitted: > 1) Memory offline: will call dissolve_free_huge_pages() to free the freed hugetlb, > and call do_migrate_range() to migrate the in-use hugetlb. Both can break the > per-node hugetlb pool, but as this is an explicit offlining operation, no better > choice. So should allow the hugetlb allocation fallback. > 2) Memory failure: same as memory offline. Should allow fallback to a different node > might be the only option to handle it, otherwise the impact of poisoned memory can > be amplified. > 3) Longterm pinning: will call migrate_longterm_unpinnable_pages() to migrate in-use > and not-longterm-pinnable hugetlb, which can break the per-node pool. But we should > fail to longterm pinning if can not allocate on current node to avoid breaking the > per-node pool. > 4) Syscalls (mbind, migrate_pages, move_pages): these are explicit users operation > to move pages to other nodes, so fallback to other nodes should not be prohibited. > 5) alloc_contig_range: used by CMA allocation and virtio-mem fake-offline to allocate > given range of pages. Now the freed hugetlb migration is not allowed to fallback, to > keep consistency, the in-use hugetlb migration should be also not allowed to fallback. > 6) alloc_contig_pages: used by kfence, pgtable_debug etc. The strategy should be > consistent with that of alloc_contig_range(). > > Based on the analysis of the various scenarios above, introducing a new helper to > determine whether fallback is permitted according to the migration reason.. > > [1] https://lore.kernel.org/all/6f26ce22d2fcd523418a085f2c588fe0776d46e7.1706794035.git.baolin.wang@linux.alibaba.com/ > Signed-off-by: Baolin Wang Reviewed-by: Oscar Salvador > +static inline bool htlb_allow_alloc_fallback(int reason) > +{ > + bool allowed_fallback = false; > + > + /* > + * Note: the memory offline, memory failure and migration syscalls will > + * be allowed to fallback to other nodes due to lack of a better chioce, ^ choice -- Oscar Salvador SUSE Labs