From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (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 A29DD72617 for ; Sun, 31 May 2026 08:48:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780217318; cv=none; b=BvLXFpqds0pYfY9wRrH4kJ79p4300tCWNo3KomZDokytrCAo7S1KKFC/XuruZ2ie3rK3y7M83+TNCAd3c/UzKdyyoo2EYPMsHyQEpzS5YvTrtjYEGkKKBpcsDssuA/IMbi7xq84DziWJ1+HmDrsmH5xWOdDJcPdamPFscPV63xk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780217318; c=relaxed/simple; bh=uSedyu6fa22/scmtGFWpkpwKG/xroOzUSAdrt+6hLoE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Aqvt2fU6HaUiKasxusIHul/Smu8j8Y8WKmVNC0oH8tP5NRMyFF1OjSQxACL1Xhj2PHwXXHn/Msl08zGa+jmGY3wf4PdYrUFZG2QeR5FMs87yHsS3v1UGiYj/UjxcR6PsIiKdT7HJBv4VVu1sWYCzSRlx42klI81+U/5GolezCDA= 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=aoIoHeGS; arc=none smtp.client-ip=95.215.58.187 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="aoIoHeGS" Message-ID: <6a9f062c-8376-4f83-90a9-8b167f925dc6@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780217312; 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=NtWyv+l/PUjKD80QEnpdDAWmHtcb20b8E/xmF2pmiZc=; b=aoIoHeGSPv7WJAUGcwp8gvMotVzsI7iE0R9cK8zt8tCXV44otjV2XtrKmsWdhCusYmakor 0G8XAsjLn21UL2vyqYY9VyPR0mcD7GaqVNcRo7DEf9pLj1qvz2RziNjQmJnHOjSQwtNeav STvc2+9ZkdHUwWEQ6I4akRieqYKUEvw= Date: Sun, 31 May 2026 16:48:17 +0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support To: npache@redhat.com Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com References: <20260522150009.121603-12-npache@redhat.com> <20260531071845.10875-1-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: <20260531071845.10875-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/5/31 15:18, Lance Yang wrote: > > On Fri, May 22, 2026 at 09:00:06AM -0600, Nico Pache wrote: > [...] >> @@ -1587,10 +1749,11 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, >> if (result == SCAN_SUCCEED) { >> /* collapse_huge_page expects the lock to be dropped before calling */ >> mmap_read_unlock(mm); >> - result = collapse_huge_page(mm, start_addr, referenced, >> - unmapped, cc, HPAGE_PMD_ORDER); >> - /* collapse_huge_page will return with the mmap_lock released */ >> + nr_collapsed = mthp_collapse(mm, vma, start_addr, referenced, >> + unmapped, cc, enabled_orders); >> + /* mmap_lock was released above, set lock_dropped */ >> *lock_dropped = true; >> + result = nr_collapsed ? SCAN_SUCCEED : SCAN_FAIL; > > Hmm ... don't we lose the allocation-failure result here? > > Previously collapse_scan_pmd() propagated SCAN_ALLOC_HUGE_PAGE_FAIL from > collapse_huge_page(), so khugepaged would call khugepaged_alloc_sleep() > in khugepaged_do_scan(). > > Now if allocation fails and nr_collapsed stays 0, we just return > SCAN_FAIL. So we won't back off via khugepaged_alloc_sleep() anymore? Looks like this is a more general issue with mthp_collapse() only returning nr_collapsed. For example, SCAN_PMD_MAPPED used to be propagated too, and madvise_collapse() treats that as success. With the new code, if nothing was collapsed by this call, that can also become SCAN_FAIL ... So I think we should keep both. Cheers, Lance