From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C12361925BC for ; Mon, 8 Sep 2025 07:51:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757317873; cv=none; b=RtBmdk2VTQnL2sqPTEP2eeOWlXtxj25TslB4wGhEm9zHyVS/KOShtZDPEzkNbCrrzIWzTYVbWDoZ3X1krahsez2TDF1H1zHuGHuxCOx9vmoHk3rvqj0/dp0GxYShHvRxdPrE8TC0i6cs3wkXttY8pd0EIN7XNZIvRh4GwXpa+AE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757317873; c=relaxed/simple; bh=AMr9tSIiW0pm9GEQStKfofummy2PPI2G3G24bIrwHgQ=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=FYj4QrkKgg+j9vST+qhlNo81E3N4VbTj6IQ2X6LQxSBnLzGk1Lgesrml+EIzQqxqk7znidDfNaMXXslbR5E/oDL/CA3OCIaaUyhr45dS57lnTYGK8aSqVRSndlW7J3PH1BkQXJVhEQa8usTma/tDHRRBehjH6R42KcXRLWomTKU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9C6E11692; Mon, 8 Sep 2025 00:51:02 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (MacBook-Pro.blr.arm.com [10.164.18.52]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A843E3F63F; Mon, 8 Sep 2025 00:51:06 -0700 (PDT) From: Dev Jain To: akpm@linux-foundation.org, david@redhat.com, kas@kernel.org, willy@infradead.org, hughd@google.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, richard.weiyang@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dev Jain Subject: [PATCH v2 0/2] Expand scope of khugepaged anonymous collapse Date: Mon, 8 Sep 2025 13:20:26 +0530 Message-Id: <20250908075028.38431-1-dev.jain@arm.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Currently khugepaged does not collapse an anonymous region which does not have a single writable pte. This is wasteful since a region mapped with non-writable ptes, for example, non-writable VMAs mapped by the application, won't benefit from THP collapse. An additional consequence of this constraint is that MADV_COLLAPSE does not perform a collapse on a non-writable VMA, and this restriction is nowhere to be found on the manpage - the restriction itself sounds wrong to me since the user knows the protection of the memory it has mapped, so collapsing read-only memory via madvise() should be a choice of the user which shouldn't be overridden by the kernel. Therefore, remove this constraint. On an arm64 bare metal machine, comparing with vanilla 6.17-rc2, an average of 5% improvement is seen on some mmtests benchmarks, particularly hackbench, with a maximum improvement of 12%. In the following table, (I) denotes statistically significant improvement, (R) denotes statistically significant regression. +-------------------------+--------------------------------+---------------+ | mmtests/hackbench | process-pipes-1 (seconds) | -0.06% | | | process-pipes-4 (seconds) | -0.27% | | | process-pipes-7 (seconds) | (I) -12.13% | | | process-pipes-12 (seconds) | (I) -5.32% | | | process-pipes-21 (seconds) | (I) -2.87% | | | process-pipes-30 (seconds) | (I) -3.39% | | | process-pipes-48 (seconds) | (I) -5.65% | | | process-pipes-79 (seconds) | (I) -6.74% | | | process-pipes-110 (seconds) | (I) -6.26% | | | process-pipes-141 (seconds) | (I) -4.99% | | | process-pipes-172 (seconds) | (I) -4.45% | | | process-pipes-203 (seconds) | (I) -3.65% | | | process-pipes-234 (seconds) | (I) -3.45% | | | process-pipes-256 (seconds) | (I) -3.47% | | | process-sockets-1 (seconds) | 2.13% | | | process-sockets-4 (seconds) | 1.02% | | | process-sockets-7 (seconds) | -0.26% | | | process-sockets-12 (seconds) | -1.24% | | | process-sockets-21 (seconds) | 0.01% | | | process-sockets-30 (seconds) | -0.15% | | | process-sockets-48 (seconds) | 0.15% | | | process-sockets-79 (seconds) | 1.45% | | | process-sockets-110 (seconds) | -1.64% | | | process-sockets-141 (seconds) | (I) -4.27% | | | process-sockets-172 (seconds) | 0.30% | | | process-sockets-203 (seconds) | -1.71% | | | process-sockets-234 (seconds) | -1.94% | | | process-sockets-256 (seconds) | -0.71% | | | thread-pipes-1 (seconds) | 0.66% | | | thread-pipes-4 (seconds) | 1.66% | | | thread-pipes-7 (seconds) | -0.17% | | | thread-pipes-12 (seconds) | (I) -4.12% | | | thread-pipes-21 (seconds) | (I) -2.13% | | | thread-pipes-30 (seconds) | (I) -3.78% | | | thread-pipes-48 (seconds) | (I) -5.77% | | | thread-pipes-79 (seconds) | (I) -5.31% | | | thread-pipes-110 (seconds) | (I) -6.12% | | | thread-pipes-141 (seconds) | (I) -4.00% | | | thread-pipes-172 (seconds) | (I) -3.01% | | | thread-pipes-203 (seconds) | (I) -2.62% | | | thread-pipes-234 (seconds) | (I) -2.00% | | | thread-pipes-256 (seconds) | (I) -2.30% | | | thread-sockets-1 (seconds) | (R) 2.39% | +-------------------------+--------------------------------+---------------+ +-------------------------+------------------------------------------------+ | mmtests/sysbench-mutex | sysbenchmutex-1 (usec) | -0.02% | | | sysbenchmutex-4 (usec) | -0.02% | | | sysbenchmutex-7 (usec) | 0.00% | | | sysbenchmutex-12 (usec) | 0.12% | | | sysbenchmutex-21 (usec) | -0.40% | | | sysbenchmutex-30 (usec) | 0.08% | | | sysbenchmutex-48 (usec) | 2.59% | | | sysbenchmutex-79 (usec) | -0.80% | | | sysbenchmutex-110 (usec) | -3.87% | | | sysbenchmutex-128 (usec) | (I) -4.46% | +-------------------------+--------------------------------+---------------+ --- Based on today's mm-new. v1->v2: - Replace non-writable VMAs with non-writable PTEs to be more specific - Add cover letter RFC->v1: - Drop writable references from tracepoints RFC: - https://lore.kernel.org/all/20250901074817.73012-1-dev.jain@arm.com/ Dev Jain (2): mm: Enable khugepaged anonymous collapse on non-writable regions mm: Drop all references of writable and SCAN_PAGE_RO include/trace/events/huge_memory.h | 19 ++++++------------- mm/khugepaged.c | 23 +++++------------------ 2 files changed, 11 insertions(+), 31 deletions(-) -- 2.30.2