From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 0B2CF2D7814 for ; Thu, 2 Jul 2026 01:47:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782956882; cv=none; b=tccjQmaqaG4fRVkmBOblrej8uod4DOAUvOof/WWRdiKeMW/onzJV3oihAWspk91PO4xvF7XQ9Di2e/5otCsXhyhwEJKyW2viLur0VGr0sVVApzSUzHuXBTmd8zncjgZV0dsXko80C25htcrEmqmOvS8LwM2I/8k72dCyJyIwOSc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782956882; c=relaxed/simple; bh=vL19Y66aq34h6lqefzTPMlw6YHkIm12+EbTAWK8cCro=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MlPXOeNRb/s3ENNrCX4at2dQIEBzaYu2cIYkImVqCmissXaiA6HfZ2TjnyP5kbZK7takkCTRVIPaemd+iFlee0IDP38nij6Xlui1zoThj4yEmxc9gHaK5dKuxNcL5Dj0lWK5kiTBQ4LQMtsB5DT/jNgmP3HDDftYLSDYlRXoKOw= 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=ZFj8EC9C; arc=none smtp.client-ip=95.215.58.174 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="ZFj8EC9C" Message-ID: <5af860ed-e468-495b-905e-5571bf7344af@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782956867; 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=JADcuSn/VPIsOHwuCi62daxla5bBVdR5HLrgcBe0R44=; b=ZFj8EC9C00SOAkiPd9aM7NmWzeXHYvQayP7DAeln2p7O6oY0pn46TFCduoAzBHEbZwdunE d6YaQcpaVWFusEmmmz55uoGwcr0BNfZFcL6jWmXkx3vyMsFm+hgvh6kWEBL83KUzjyTeKF j3I0zb2aV3VH+Bg+ZkWgp5I75KWH2es= Date: Thu, 2 Jul 2026 09:47:25 +0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [Patch mm-hotfixes v5] mm/page_vma_mapped: fix device-private PMD handling To: Klara Modin Cc: david@kernel.org, richard.weiyang@gmail.com, akpm@linux-foundation.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, balbirs@nvidia.com, sj@kernel.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260701163356.22936-1-lance.yang@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/7/2 00:46, Klara Modin wrote: [...] >>>> >>>> My only guess here would be that the compiler evaluates >>>> !softleaf_is_migration(entry) to always be true and optimises away the >>>> !check_pmd(softleaf_to_pfn(entry), pvmw) which is why this worked >>>> before? >>> >>> Weird, we enter this path only with >>> >>> pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || >>> pmd_is_device_private_entry(pmde) >>> >>> If any one of these would compile for !CONFIG_TRANSPARENT_HUGEPAGE that would be >>> odd. >>> >>> pmd_is_device_private_entry() is hard-coded to false unless >>> CONFIG_ARCH_ENABLE_THP_MIGRATION. Which is only selected with >>> ARCH_ENABLE_THP_MIGRATION. >>> >>> pmd_trans_huge() as well. >>> >>> Maybe it's struggling with pmd_is_migration_entry() on some (older) compilers? >>> (not innlining stuff and not properly optimizing it out). > > It's a GCC 16 cross-compiler for armv6 so I wouldn't call it old :) > >>> >>> The whole conditional must be optimized out. >> >> Right. Kinda weird if compiler didn't fold >> >> pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || >> pmd_is_device_private_entry(pmde) >> >> away here ... >> >>> We could check for IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) right at the start >>> to make it easier for the compiler: >> >> +1, explicit THP guard should do the trick :) >> >>> if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) && >>> (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || >>> pmd_is_device_private_entry(pmde))) { >>> >>> >> >> Klara, could you try with this change and see if it fixes the build? >> >> Thanks, Lance > > This does indeed make it build. Good to know, thanks for testing!