From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 47ABA51475A for ; Wed, 9 Sep 2026 15:17:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788967033; cv=none; b=Fg80+IfLqmVe7Wfr/0DbHL5ji9QQpDq/8Lf4/1/mRytlxyR9mRraiHiyGzsEDbjRyWw9OM1wl+jFcepwCs/WfbSgr5dcor3Zw+S3dDC7qlxHbGYQJQ6j0F45/981OhJOnkfMzJeXzV89BHZ1yYLfOhwngaLqJKlLgQyBcLD+M1g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788967033; c=relaxed/simple; bh=9sJRY1D/bhmVnNJ9xtYfrHKaRhV628XmAaXzS9iY6OM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=p0dCZV6Wp0PuwPlmxSEyvJlFVfGE0FoMJyGlK/iarvm8nBApD8HEXh/fPKx1z+prMYnYnT5goSH2b4oVHsDODBOzRSclo7JDRNcW3TJ9nuLxF+66IZPS8G5w27IlIPdohbu/L173yZK5to0y40xz4wkaJPLNzqdAcBCCF0igI2I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bJwf8pIJ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bJwf8pIJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ABB451F00A3A; Wed, 9 Sep 2026 15:17:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788967031; bh=yMpwt5jk08Xm5DwGlNwjV3jDkm0c7VN2w5E4BNJFyJg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bJwf8pIJ4fb1VkYkGkn9jh7csMatHoWRsh0+x4jVPH0Xe9SW2SoX9ayXbWiM1jjfx ZXeT4klcknZmthc19OrMRbF2BfbAWxXM84R4e6zrJEKFF+G9OyaX/X7nRQ9SECaAaG FaPkfhLbpb2f941jVa2RWNEaQYZzOfX5ba5d+eSI+Li12enPOuHkTPVHeCgm4drkhC oDYHixZdVpzaIHG1i3Ylq0eWuQmM2mt2KAKLOp2EkANf4qRa54hMQ9jVE/RRti3DKz p7qho55XczRF5YGnwYYsa1XCBpuCil2sblZsIrRL3PVE2i6xWNeHm13J/mJhc32VOO QlJrT1YNvbzkw== Message-ID: <91cf8129-d705-4ebd-b420-129bab7ed261@kernel.org> Date: Wed, 9 Sep 2026 17:17:08 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/ksm: trylock the mmap lock in the unstable tree walk To: xu.xin16@zte.com.cn, xialonglong2025@163.com Cc: akpm@linux-foundation.org, linux-mm@kvack.org, chengming.zhou@linux.dev, linux-kernel@vger.kernel.org, xialonglong@kylinos.cn References: <20260909110228828hKTCgUeuZkOujOBaVtUcL@zte.com.cn> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit >> index 49d48d1e0998..3cfb09a926ff 100644 >> --- a/mm/ksm.c >> +++ b/mm/ksm.c >> @@ -820,7 +820,14 @@ static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item) >> struct folio_walk fw; >> struct folio *folio; >> >> - mmap_read_lock(mm); >> + /* >> + * We trylock because we don't want ksmd to wait for an mm that is >> + * busy changing its memory layout: we prefer to skip this page and >> + * let the next full scan retry it, like the folio trylock in >> + * try_to_merge_one_page(). >> + */ >> + if (!mmap_read_trylock(mm)) >> + return NULL; >> vma = find_mergeable_vma(mm, addr); >> if (!vma) >> goto out; >> -- >> 2.43.0 > Sorry, NACK Agreed. Likely the answer is to switch to per-vma locks here. All we do is a folio_walk_start() to look up a page, that's not too crazy :) -- Cheers, David