From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-170.mta0.migadu.com (out-170.mta0.migadu.com [91.218.175.170]) (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 12B1F304BB3 for ; Thu, 30 Apr 2026 08:15:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777536928; cv=none; b=afd97a8Slg/4n++nd8DVbVnPP0Avk/4yfaq9kGfozzzAPigOCNmUhV2Ch/LDgT/exetE1L4u4gtELAc8PNe8FHHJO3QXJhtzNI+T8wZF481ndMidCdhjcISx3z+nNWqb9Cseu7CzWhK5TlYVMLLNMXDcENzB8V/PlkWn+OCQE0Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777536928; c=relaxed/simple; bh=HZStE9y05jjfjS8t2b6sKPgf7XpWSEdHck04VxGFE84=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JQMv7tn0AI1dcNBkSkn1usMg90dgNdB1WpJPLqneI6p1C3M6KSolKAttZfBvJ/RQHyNXlLc5cY6DRK35MkiRuTd0bVUp3O+gzfCYS/vAVsbtAzbmpDhOVlf0YvZyIMUF+7reyaiDdT1irh3pgpwt0KjYU0vDpqv3L0XS1r9S5gw= 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=sIrfZG4L; arc=none smtp.client-ip=91.218.175.170 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="sIrfZG4L" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777536924; 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=QeKSgDzY/uWbLPbJzTnzMQBUL5j9ZNsCB3b2Vb5/Nio=; b=sIrfZG4LUjkE03kAS3LxgPB4QZxWd7q3bavgFesOIcjtc2+9Fzxse9zeeU0zOGMQoNPZQK PdITEcGuRG8GcCeum0HuZcWpQsheDZiVU6ACTRMxddDCkYZ+1/fneY8098gWj8SPwiax9E NJbCSUbCJdb1tPcwENLIM6BMg6Fb0CE= Date: Thu, 30 Apr 2026 16:15:13 +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> <37531e17-2a4a-44f5-af61-667331444ca2@linux.dev> <4807181d-c111-5568-b040-140706e56b4f@loongson.cn> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <4807181d-c111-5568-b040-140706e56b4f@loongson.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2026/4/30 16:09, Bibo Mao wrote: > > > On 2026/4/30 下午3:16, Lance Yang wrote: >> >> >> 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 > yes, this patch solves the problem. I do not subscribe linux- > mm@kvack.org mailing list, please feel free to add > > Tested-by: Bibo Mao Thanks for testing!