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Tue, 27 Dec 2022 17:24:45 -0800 (PST) Date: Tue, 27 Dec 2022 17:24:44 -0800 (PST) From: David Rientjes To: Yin Fengwei cc: riel@surriel.com, nathan@kernel.org, Andrew Morton , shy828301@gmail.com, Matthew Wilcox , kirill.shutemov@intel.com, ying.huang@intel.com, feng.tang@intel.com, zhengjun.xing@linux.intel.com, linux-mm@kvack.org Subject: Re: [RFC PATCH] mm/thp: check and bail out if page in deferred queue already In-Reply-To: <20221223135207.2275317-1-fengwei.yin@intel.com> Message-ID: <677d82d8-f8c9-9a60-3af0-e7931c7728c6@google.com> References: <20221223135207.2275317-1-fengwei.yin@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C921B180004 X-Rspam-User: X-Stat-Signature: 17y14yqbp85sr3waugej47bxwi4xwjk7 X-HE-Tag: 1672190687-61102 X-HE-Meta: U2FsdGVkX1+RgO3TLAgqc2ZY+mig7qXKq0VtoAPwpfoR5I7DNgUBnkG2pJHW4OFC8Xegf98zR7d+kMqde0UyC/aKjpB1QSCaBQBaVXVE7uti8t2ndObRA3m5taaVyXtqALmd8qb2timOh39inAYoveBTKXfytAKIyCFY5fctF5OPEvfQ1+flIiAEHVqcgF+kSbvivMV1JCi1p/hT6hsZal3MPYqnAJ3qgj6fiTkeVepOeMdwg3qmzWTuwFi5N8jKA4+AqfzmKIysHDTnWhYnU3Fwnsx6uVsKE3sdFWVeG+O2M/NQPvlMHGUSZoHqwF82PopigV3g1rsRLqi5BudZoXjELXfwY2C3Hmq98S61uFLHyqPsevnxxkuqp8d/+dAWr6OHO9GLg+tLfF0R38PkPL+rs5LzYcopKZG4ZFaWi1mPIvnNI19UbOJt6JYY4ygBsEe9Zp/FfuGMhx5b7x7S9L/vaxat7utlnSkEwczyWH01sH8bhmrBD3EjYOsnCF6Xvyemr6LvIEgyAzDAdofJzTtTPmZaOtOlfWdlAIx/waD9Xk/1QhEf9LDp9YvitHmQzr5kAyQHAXKT+fnC+GB2Q71LC4S6OaJTpOzIkTTFVkdLZM6VUl7IQ9m+OJiUVGue7sOXBA71Ti05Oxn29EnT4Sk7I+ELC0psTP16Q48+EzQ93xU/nWrJClORbix0cQndydgovThVMfA9K1CRVjjIoIwRNhRJp55fQkrjB2Az6CqHp6zh4ZRMtGuxo0v3yy1EaiX8eiggwz0Fh90jSz8lkvEuTonJl+3theiRADPBims64jOR8wplIDoBy9Y++dO31sMOCe/F02YgLJO8nxGOzXT4DUsHIr0F3bLxbYDSOPznmWyNiqe7ju4APGFsMfrtgf5WBzcVGSiwTguMX8QRmBJRDHk5bCUUB3mKGZPkluKJf9GcsonSDDiM80oN+0E3TH3nzTpj+2hK/6CCu1y vzQ1SLC6 HUx0plAGDd8+hohBxAA0G6gVhFafUHq+raOybZEo00afOYNoQ87elUiVKtg== 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 Fri, 23 Dec 2022, Yin Fengwei wrote: > Kernel build regression with LLVM was reported here: > https://lore.kernel.org/all/Y1GCYXGtEVZbcv%2F5@dev-arch.thelio-3990X/ > with commit f35b5d7d676e ("mm: align larger anonymous mappings on THP > boundaries"). And the commit f35b5d7d676e was reverted. > > It turned out the regression is related with madvise(MADV_DONTNEED) > was used by ld.lld. But with none PMD_SIZE aligned parameter len. > trace-bpfcc captured: > 531607 531732 ld.lld do_madvise.part.0 start: 0x7feca9000000, len: 0x7fb000, behavior: 0x4 > 531607 531793 ld.lld do_madvise.part.0 start: 0x7fec86a00000, len: 0x7fb000, behavior: 0x4 > > If the underneath physical page is THP, the madvise(MADV_DONTNNED) can > trigger split_queue_lock contention raised significantly. perf showed > following data: > 14.85% 0.00% ld.lld [kernel.kallsyms] [k] > entry_SYSCALL_64_after_hwframe > 11.52% > entry_SYSCALL_64_after_hwframe > do_syscall_64 > __x64_sys_madvise > do_madvise.part.0 > zap_page_range > unmap_single_vma > unmap_page_range > page_remove_rmap > deferred_split_huge_page > __lock_text_start > native_queued_spin_lock_slowpath > > If THP can't be removed from rmap as whole THP, partial THP will be > removed from rmap by removing sub-pages from rmap. Even the THP > head page is added to deferred queue already, the split_queue_lock > will be acquired and check whether the THP head page is in the queue > already. Thus, the contention of split_queue_lock is raised. > > Before acquire split_queue_lock, check and bail out early if the THP > head page is in the queue already. The checking without holding > split_queue_lock could race with deferred_split_scan, but it doesn't > impact the correctness here. > > Test result of building kernel with ld.lld: > commit 7b5a0b664ebe (parent commit of f35b5d7d676e): > time -f "\t%E real,\t%U user,\t%S sys" make LD=ld.lld -skj96 allmodconfig all > 6:07.99 real, 26367.77 user, 5063.35 sys > > commit f35b5d7d676e: > time -f "\t%E real,\t%U user,\t%S sys" make LD=ld.lld -skj96 allmodconfig all > 7:22.15 real, 26235.03 user, 12504.55 sys > > commit f35b5d7d676e with the fixing patch: > time -f "\t%E real,\t%U user,\t%S sys" make LD=ld.lld -skj96 allmodconfig all > 6:08.49 real, 26520.15 user, 5047.91 sys > > Signed-off-by: Yin Fengwei Acked-by: David Rientjes