From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-185.mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (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 EFE3A335564 for ; Thu, 30 Apr 2026 07:16:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777533387; cv=none; b=akKWxWkh1vG7GWWpp26+Iui8YEcWdu4pofzlH7SgI87Ylugv1P3/JdEmlJJ70Ld7HSP7alJZ8XH9iQhGArnwwSM4etGaHsCJ82g4sBz2+dr/nPEcSRGg1tPTcHvYqnlPORwn9xt6CmiJE0wOtb89QL+xQXio4960hnb4RxQRVoc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777533387; c=relaxed/simple; bh=gFEpUnimrYaJ1oGzEyYxlDVGFWR9bUhB2614XScDa4M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JO5VZN7pVKBRruRfVFexWpVG+HcwG+/iFu3kfkqhBYKQNFQDiRM0tUn68LnKThvSerUuT9xgqnbdUf/yhSztyvQtO/o5FOk6ZsZ46iVQKFisTbqhVcb8FIECuewtEQfZsieNMVavKTCfA/Wv8E4AC4jRhl1x2NLWMTmHUYtj6tI= 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=VmGGCE3h; arc=none smtp.client-ip=91.218.175.185 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="VmGGCE3h" Message-ID: <37531e17-2a4a-44f5-af61-667331444ca2@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777533383; 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=nMif5YaFdMKdpNExsymbLQ/P3y0xhUVDlzi/+K+RFcU=; b=VmGGCE3hw6fcephCk88ccwFrZv4tJWQzk03j4PbAqmaZWra98yAYE9+jf/y3l24xYDaQAN kU/BEfw7RCxyiiuDgXV9/NiAaHE4G21dRSeQT+XDxkf2aokoEATDdJ/Hk2z0wBmrrGD4Ly VwLfuPqsWbgQFvxqZM7lRhVB2LcFbEM= Date: Thu, 30 Apr 2026 15:16:13 +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/huge_memory: skip huge_zero_pmd in zap_huge_pmd_folio() Content-Language: en-US To: Bibo Mao Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260430070217.39679-1-lance.yang@linux.dev> <6cdeb3e7-c399-4ead-e809-44e3d4d84bc7@loongson.cn> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <6cdeb3e7-c399-4ead-e809-44e3d4d84bc7@loongson.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2026/4/30 15:05, Bibo Mao wrote: > > > On 2026/4/30 下午3:02, Lance Yang wrote: >> >> On Thu, Apr 30, 2026 at 02:34:20PM +0800, Bibo Mao wrote: >>> >>> >>> On 2026/4/30 下午12:28, Lance Yang wrote: >>>> >>>> On Thu, Apr 30, 2026 at 12:11:20PM +0800, Bibo Mao wrote: >>>>> when executing command "make check" with qemu software, there is >>>>> error report like this: >>>>> BUG: Bad rss-counter state mm:00000000972846bc type:MM_FILEPAGES >>>>> val:-4096 Comm:bios-tables-tes Pid:27802 >>>>> BUG: Bad rss-counter state mm:00000000752180c5 type:MM_FILEPAGES >>>>> val:-2048 Comm:worker Pid:27815 >>>>> BUG: Bad rss-counter state mm:000000009c2f6a61 type:MM_FILEPAGES >>>>> val:-2048 Comm:qom-test Pid:27825 >>>> >>>> Good catch! >>>> >>>>> The problem is that when application exits, rss counter is calculated >>>>> with huge_zero_pmd huge page, instead it should be skipped. >>>> >>>> Looks like the same problem[1] we discussed recently. >>>> >>>> [1] https://lore.kernel.org/linux-mm/74a75b59-2e13-3985-ee99- >>>> d5521f39df2a@google.com/ >>>> >>>>> Signed-off-by: Bibo Mao >>>>> --- >>>>> mm/huge_memory.c | 3 +++ >>>>> 1 file changed, 3 insertions(+) >>>>> >>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>>> index 970e077019b7..3cbea344d4a2 100644 >>>>> --- a/mm/huge_memory.c >>>>> +++ b/mm/huge_memory.c >>>>> @@ -2423,6 +2423,9 @@ static void zap_huge_pmd_folio(struct >>>>> mm_struct *mm, struct vm_area_struct *vma, >>>>> { >>>>>     const bool is_device_private = folio_is_device_private(folio); >>>>> >>>>> +    if (is_huge_zero_pmd(pmdval)) >>>>> +        return; >>>>> + >>>> >>>> The huge zero PMD should not be returned by vm_normal_page_pmd() or >>>> vm_normal_folio_pmd() as a normal folio. If it reaches >>>> zap_huge_pmd_folio(), we already made the wrong normal-vs-special >>>> decision ... >>>> >>>> So I don't think we should special-case it in zap_huge_pmd_folio(). >>>> That >>>> only avoids this RSS decrement :) >>>> >>>> Could you please check whether the fix[2] also fixes your QEMU test? >>>> >>>> [2] https://lore.kernel.org/linux-mm/ea1453a6-14c9-4334- >>>> ac7e-2758586393b2@kernel.org/ >>> yes, I think it will solve this problem. >>> >>> Only that I think that there should be tlb flush operation after >>> pmdp_huge_get_and_clear_full() even with huge_zero_pmd page, so >>> tlb_remove_page_size() should be called. Is that right? >> >> Calling tlb_remove_page_size() is not necessary there :) >> >> zap_huge_pmd() already marks the PMD range for TLB invalidation right >> after clearing the entry: >> >>     orig_pmd = pmdp_huge_get_and_clear_full(...); >>     tlb_remove_pmd_tlb_entry(tlb, pmd, addr); > Yes, it is. I forget the tlb_flush_pmd_range() calling in > tlb_remove_pmd_tlb_entry(). > > So the fix solves this problem. And thanks for your explanation. If possible, can you test the fix[1] with your QEMU workload and provide a Tested-by? That would be very helpful :D [1] https://lore.kernel.org/linux-mm/4d950326-6944-409b-b108-a4e67256857f@kernel.org/