From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.17 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794296614; b=NBlhqgFiNr7/k54F18SVq7LPmcKExBuLzfR7IwzUrlaJrGmP8+N/NXgPwtpj8+8uyZWG ios0FmOgAeJw/64y8mngkNXNZESEX2M3fLbvZS9TT3LFoWVQwkiRb4WwtN1lt6lRvBDa2 6wXTmu1FpiFkqKNXKc7YqPajFBqaaGRC6eMRtCpnlZcdDxh4BvKZPVEyO44f4nvTquU61 YYO92ENozNG0CeQUYPzYOUjhtiMkF+DzxX0k0NoC5JQpScf/iebB/aAaFQ5eIcRep1FSs yXabB7QxUKc/GNjmV7TARwos/dzXkZA6iiDn0IIyZPrMl8sIqO6DC5F8PZXZVJGmIfw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794296614; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-Id: X-Mailer:MIME-Version:Content-Type:Content-Transfer-Encoding; bh=yIKrqUa698jtkq4S+tNE275rUsH+jw4iBZHp6nea714=; b=yzeSpYrrDIwbQKAgMdpWf3xUGYLb5Nrq/Pj4NiqlvYDJgwrmjaEyQQdnsw1X2lq+iPiR aZetjYO/WAtmSoNr3roVHa2f/rFqkTIUVtQokX3Xb0pd3m3+qxG1Gu2Ms3M10Q+FqfJNC pq2BaqzeN6DheHbmh23sEpmJYEcQHfSlKP1KPvyneU3YOukgEMFoG/aURUT1noSnIBXku 2JjHvs/gDpP4RWzV+HNWMxiU3iKikWygCR5qfPKTil1FReb8b8xcsToyAONChN+HS8rzK uD63JBvqx9k4/APEAtYcwEMDQ5J12tNQaLGRdgHe5CVYvX3QfwXL5xakcZNl0Noe3kQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=aOeOHpYh; arc=none smtp.remote-ip=95.215.58.17 Received: from mta1.migadu.com (out-17.mta1.migadu.com [95.215.58.17]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C3D2606A321 for ; Tue, 10 Nov 2026 07:43:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 4C3D2606A321 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=aOeOHpYh X-Envelope-To: linux-kselftest@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=PqgEJ1qFzNTxxzLoVkBM63dh+frDqe4TYsbrUm3uZw4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794296611; v=1; x=1794901411; b=aOeOHpYhP4JC5moGBDMfC0Xadr1TZnY18hEpwkIH/tKibJ4X9IS1g3lIjbFEI6l/2Lvafrt4 VBLSoGU5m2Dx5iOUydtuPRQ/N/OnSNUqE9DIJ11/bfgAIwrRKSR0pE8QOcA9VkI3g+C5XhR2ee6 qsmiud3Q4h7Kx7WPVxjN7fLQ= X-Envelope-To: linux-kselftest@vger.kernel.org Received: by mta11.migadu.com with ESMTPS id 9b3c4fed74b348b8; Tue, 10 Nov 2026 07:43:31 +0000 X-Mizu-Trace-ID: 9b3c4fed74b348b8 X-Migadu-Flow: FLOW_OUT From: "Xu Xin (vivo)" To: David Hildenbrand , Xu Xin , Chengming Zhou , Andrew Morton , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jonathan Corbet , Jinjiang Tu , Qiliang Yuan Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Huan Yang , Wang Xiao Subject: [PATCH v2 0/4] KSM: introduce only_merge_zero_pages Date: Tue, 10 Nov 2026 15:43:12 +0800 Message-Id: <20261110074312.219847-1-xu.xin@linux.dev> X-Mailer: git-send-email 2.34.1 X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi all, This series adds a new KSM sysfs attribute, only_merge_zero_pages, which makes ksmd merge only empty (zeroed) anonymous pages with the kernel zero page and skip the stable/unstable trees for pages that carry data. Patch 1 adds the attribute and the early return in cmp_and_merge_page(). Patch 2 (co-developed with Jinjiang Tu) goes one step further and skips non-zero pages already in the scan path, before an rmap_item is allocated for them, which is what makes the mode practical on large-memory workloads with mostly non-mergeable anonymous memory. Patch 3 consolidates the ksm_stat readers in vm_util.c into a single ksm_get_self_stat() helper (pure refactor). Patch 4 adds a functional selftest. Changelog ========= v1 -> v2 - Patch 1: Take ksm_thread_mutex around the check-and-set in both use_zero_pages_store() and only_merge_zero_pages_store(), so that a concurrent write to the two attributes cannot leave use_zero_pages=0 and only_merge_zero_pages=1, a state in which ksmd would scan and checksum pages but never merge any. - New patch 2, 3 and 4 are added. Motivation ========== On an Android device, I measured the KSM savings potential on 15.7 GiB RAM, ~1100 processes, a typical usage session with several video apps running) using a userspace survey tool that walks /proc//maps + /proc//pagemap, deduplicates anonymous pages by their physical frame number (PFN), and hashes page contents to find identical pages. Key results (two samples taken 10 minutes apart): Category Resident Savings (upper bound) ------------------- --------- --------------------- anon, non-zero pages 2.9G 67-74 MiB (2.3-2.4%) anon, zero pages - 281-424 MiB (9.5-13.9%) In other scenario with a MySQL instance from huawei, there are around 15 GB consumed by hashtables, which contain many zero-filled pages that are eligible for merging to reduce memory footprint [1]. [1] https://lore.kernel.org/all/2a642af6-b97a-4f24-9889-1844812de4cc@huawei.com/ Xu Xin (vivo) (4): ksm: add only_merge_zero_pages to merge only empty anonymous pages ksm: skip rmap_item allocation for non-zero pages under only_merge_zero_pages selftests/ksm: consolidate ksm_stat readers into ksm_get_self_stat() selftests/ksm: add test for only_merge_zero_pages Documentation/admin-guide/mm/ksm.rst | 40 ++++- mm/ksm.c | 149 ++++++++++++++++++ .../selftests/mm/ksm_functional_tests.c | 135 ++++++++++++++-- tools/testing/selftests/mm/vm_util.c | 40 ++--- tools/testing/selftests/mm/vm_util.h | 3 +- 5 files changed, 327 insertions(+), 40 deletions(-) -- 2.34.1