From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta1.migadu.com (out-179.mta1.migadu.com [95.215.58.179]) (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 4A8B02773CA for ; Sat, 27 Jun 2026 02:51:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782528706; cv=none; b=OowLJS7Lv72Vgz8K+iFqAigG8lD6Kmd9/J+n+qswF/r4za4rIwf8LuQcw8L6u4/N2glFVWx67F+4tQY0yrEjYM2eWIDqSj37NIeBsvuX9GMmFO0O2uLmWJOw/7RHgnGMLgz2P8agIsV426s1NqfaPQ/pLC+MDC3+uFpYhHUMU/U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782528706; c=relaxed/simple; bh=Pc6g61P+PpxGknRJgmmqIo167RjsspVtlCGIy7/VoFw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=o1UFgv6HtvFd4QjWNLjsj/7ZyBhi0KavHCwMvwa/VfcWrPep+AtEXN4cs+HHuJnDWAcMaH/RjkWABGbrh/V5RKL0Y7lIM0JSBpW7U26UA4MmdybuyJSEEzY/JKThxhNGqzm96tLo75lGAnxgoTk5ZqjSlkSoj4YOcYRcHPokn9A= 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=HzaW6oQX; arc=none smtp.client-ip=95.215.58.179 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="HzaW6oQX" Message-ID: <99fa03d6-9869-476b-a605-1ab27f13c369@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782528703; 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=BDYcE5MsrZIKnRWtwXNcAj7rSHtaafqGAtwFoyTEBR0=; b=HzaW6oQXohR6/maYtwI7n7BvwwmvGnJO/N1eUnnHpEXBW5Qyuo2NPtrEUtsoS3CdlTRLdA W2uQQ113xI/zkQsAapMbuuBudKju88XP5F5ATruxgFSHRV7RlHKH5eXdgp6KH18X2+iC2/ sy6HTHxPVGhRdLHcutYJKoJJp9tpMuQ= Date: Sat, 27 Jun 2026 10:51:27 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [Patch mm-hotfixes v4] mm/page_vma_mapped: fix device-private PMD handling Content-Language: en-US To: Wei Yang Cc: david@kernel.org, akpm@linux-foundation.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, ziy@nvidia.com, sj@kernel.org, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260626132728.77436-1-lance.yang@linux.dev> <20260627003813.ktpya35fx5doaz36@master> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <20260627003813.ktpya35fx5doaz36@master> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/6/27 08:38, Wei Yang wrote: [...] >> >> Might be good with this on top: >> >> ---8<--- >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >> index cfa1230c87bb..8b7c062bd81d 100644 >> --- a/mm/page_vma_mapped.c >> +++ b/mm/page_vma_mapped.c >> @@ -281,7 +281,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >> return not_found(pvmw); >> return true; >> } >> - /* THP pmd was split under us: handle on pte level */ >> + /* THP/device-private pmd was split under us: handle on pte level */ > > As the comment in commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration > support device-private entries") says: > > Add device-private THP support... > > Per my understanding, we first already setup mapping and "migrate" to device > memory. This looks a kind of place holder. > > Not familiar with this. Just want to clarify, we want to treat device-private > pmd as some sort of THP or not? Not a regular THP, obviously. Just the PMD-sized device-private entry case. It can be split under us too; see commit 146287290023 ("mm/huge_memory: implement device-private THP splitting"). Nothing deeper meant here. After taking PTL, if that PMD-sized entry is gone, just drop to the PTE walk. > >> spin_unlock(pvmw->ptl); >> pvmw->ptl = NULL; >> } else if (!pmd_present(pmde)) { >> --