From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) (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 AEFB11850A4 for ; Thu, 30 Apr 2026 07:02:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777532552; cv=none; b=GCl5STf4xttIQJLnXqH42GFbEZhFhBz4zJZ0UoUvJs5FbgwpbMFO82Fy98UgPxg5SMSkBF9qjEAnw5trejwOfQx8Jq9MUwVcToBD0FeCsbbKJi6Pry7k80UKjWLbtwhjWvEZRfJJJyUJ7lqnHgrsHRErevzD2qN0IcCYtGe2FoI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777532552; c=relaxed/simple; bh=gjjdXkx0+61ibPR2U+T00KNLbJ94H67OKDVV1EB0W/U=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=U2+zecLLgqHHWDeBZWJCndCcZhKOnxN7F5bGSXMMpSrjrnBn3i28HI4uofH1SnY8nuoousB/UKjv1ELeDxGTjs/f8bqL594Ftjo8mapls9nCqm9LtT8pMja0V9Y3K4PQ64f8zncie3vlewiOuco15wOh/E22NS0/pfSb8NZPAFA= 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=tWkuXsrx; arc=none smtp.client-ip=91.218.175.180 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="tWkuXsrx" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777532546; 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=XnPzbyjR2RPMnocbYTJgY5ykVBYijb42BCSHLD8WL2M=; b=tWkuXsrxh5SQivLKUD5ssncT32NSJKFFaVzBCoyNLPGomQrobwv7fdWUgoeRCujr65JgpM 0x8cfxLH8zeVfolyz3QQkTiYrkymYbDM6vL+7DpD0sLayloESPYZ0FIWe9ZT4u7UhCr1Br czHtnmha6ci4sX71feYkefSZbepLSC4= From: Lance Yang To: maobibo@loongson.cn Cc: lance.yang@linux.dev, 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 Subject: Re: [PATCH] mm/huge_memory: skip huge_zero_pmd in zap_huge_pmd_folio() Date: Thu, 30 Apr 2026 15:02:17 +0800 Message-Id: <20260430070217.39679-1-lance.yang@linux.dev> In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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); The later tlb_remove_page_size() is guarded by "is_present && folio", and is for the normal folio case after normal_or_softleaf_folio_pmd() return one :) Please correct me if I missed something :D Cheers, Lance