From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 74D0AC2EF for ; Wed, 18 Jun 2025 02:25:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750213549; cv=none; b=unBf8DsLgTfjbg9+p2hCLenjyNzKnniKFeKf5NjZJahyFdWveudl+SIJxTnWb2W4XHcrJN3gH1W+piGWRtl8syTrldsAUryWffUVQc7BlHoTvD7/h8RRjCmgwZ/wv+UGZOxuHWR2mYyj5P+YhkTBb1osTLfy4t2s2n2HuFZyjuA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750213549; c=relaxed/simple; bh=OaHgiZazmyc06LjxYXLe7izja8CfrKabh/GxjNs2paw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=onFa1WRPTc6m6tmiDvTWVvJ8DH+ZoPQqmdnauWnptkjQjuxWWMXlp++TH9+ixBk8hWIaUIb/mWtPywBBncCQMfsXIURHc/zywMW1gK/bmh0ajTzDl1UK2OVndeagPWQJ9QsfF71C31OD1SKem4rr+BjnwMBF5XpRDHLHHo6pN10= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=olPnJ/Ft; arc=none smtp.client-ip=91.218.175.181 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) header.d=linux.dev header.i=@linux.dev header.b="olPnJ/Ft" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1750213542; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WRnT8oSN8k3lo5CGyLRxRbzv9ULV2vj8IJVFOUE6h9A=; b=olPnJ/FtjhUAXcFuf0XSpr3qb4c5xrdg+M22XKq4JMIybh8zteDsQ8Z2tnkY/S2cNc4ggi jlX4Ytm3vMiya30fLJ8CUlcma0UMwBVeduQoArL230FvZnplmF4DfSM9RsPneAuRe/uwzW EyjgsKfmraLTlrD1j/21rtXlKEvjUeg= Date: Wed, 18 Jun 2025 10:25:36 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v4] mm: use per_vma lock for MADV_DONTNEED Content-Language: en-US To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , "Liam R. Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , Suren Baghdasaryan , Lokesh Gidra , Tangquan Zheng , Qi Zheng , Lance Yang , Lorenzo Stoakes , Zi Li References: <20250607220150.2980-1-21cnbao@gmail.com> <309d22ca-6cd9-4601-8402-d441a07d9443@lucifer.local> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <309d22ca-6cd9-4601-8402-d441a07d9443@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi all, Crazy, the per-VMA lock for madvise is an absolute game-changer ;) On 2025/6/17 21:38, Lorenzo Stoakes wrote: [...] > > On Sun, Jun 08, 2025 at 10:01:50AM +1200, Barry Song wrote: >> From: Barry Song >> >> Certain madvise operations, especially MADV_DONTNEED, occur far more >> frequently than other madvise options, particularly in native and Java >> heaps for dynamic memory management. >> >> Currently, the mmap_lock is always held during these operations, even when >> unnecessary. This causes lock contention and can lead to severe priority >> inversion, where low-priority threads—such as Android's HeapTaskDaemon— >> hold the lock and block higher-priority threads. >> >> This patch enables the use of per-VMA locks when the advised range lies >> entirely within a single VMA, avoiding the need for full VMA traversal. In >> practice, userspace heaps rarely issue MADV_DONTNEED across multiple VMAs. >> >> Tangquan’s testing shows that over 99.5% of memory reclaimed by Android >> benefits from this per-VMA lock optimization. After extended runtime, >> 217,735 madvise calls from HeapTaskDaemon used the per-VMA path, while >> only 1,231 fell back to mmap_lock. >> >> To simplify handling, the implementation falls back to the standard >> mmap_lock if userfaultfd is enabled on the VMA, avoiding the complexity of >> userfaultfd_remove(). >> >> Many thanks to Lorenzo's work[1] on: >> "Refactor the madvise() code to retain state about the locking mode >> utilised for traversing VMAs. >> >> Then use this mechanism to permit VMA locking to be done later in the >> madvise() logic and also to allow altering of the locking mode to permit >> falling back to an mmap read lock if required." >> >> One important point, as pointed out by Jann[2], is that >> untagged_addr_remote() requires holding mmap_lock. This is because >> address tagging on x86 and RISC-V is quite complex. >> >> Until untagged_addr_remote() becomes atomic—which seems unlikely in >> the near future—we cannot support per-VMA locks for remote processes. >> So for now, only local processes are supported. Just to put some numbers on it, I ran a micro-benchmark with 100 parallel threads, where each thread calls madvise() on its own 1GiB chunk of 64KiB mTHP-backed memory. The performance gain is huge: 1) MADV_DONTNEED saw its average time drop from 0.0508s to 0.0270s (~47% faster) 2) MADV_FREE saw its average time drop from 0.3078s to 0.1095s (~64% faster) Thanks, Lance