From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 2DE65360EE6 for ; Sun, 31 May 2026 07:19:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780211964; cv=none; b=nK5GmYsIK6t1lhb06t15pCCGyhi6ZIfyApogUPBKgkn3b+5bRVuvMLsL+Ug29e7tBQvOEEQ0IYf2EyjoFUhpMOmz1w4aAnM3olgam3tusIx5U5TxtJVEdAo/TYBER6L8b9RNx9hOk3t8WLyod4uT2ReJ8xci6fpADqlfZzgiweQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780211964; c=relaxed/simple; bh=4oQpFIVJnyhvUIU2EIwvLfR93Esgnrj76UG6pXPvXzw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=VBNJAI9mVFdecF9o8vpRY2nc9j5ygFiKmkUj906LtcBmyAX/w4SiWJj6RaK8QZWtz1HyrxpkR++K9DeY29PWl0sAkPK0NNGFp+QahwEJ4azyyztCiihIb6gfzYmUUx3empoeK8enp0mfoGRZEcmT/lx3b2LweRVxqGd6HfFmoCs= 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=OKYxp2/e; arc=none smtp.client-ip=91.218.175.174 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="OKYxp2/e" 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=1780211958; 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=UgyOMSo1NQT9NR/s9Gmh5C++kaNJthsUpAzUGUjKh8k=; b=OKYxp2/euq94yW/BPlLJPwdiYfRQcuT145cwocxP1tMXDQnxVH8DFOnodfv1FPZXMlXLCc kRTYcgDt2gUggNPJiWjwTB5Smh2j0coJATntxq/OKgA9TmbAefd+z7fbWApU/qd8xKAYxI SMqIEnb+vlsE2yUpzPce/xXrgmk12Tc= From: Lance Yang 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, lance.yang@linux.dev, 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 Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support Date: Sun, 31 May 2026 15:18:45 +0800 Message-Id: <20260531071845.10875-1-lance.yang@linux.dev> In-Reply-To: <20260522150009.121603-12-npache@redhat.com> References: <20260522150009.121603-12-npache@redhat.com> Precedence: bulk X-Mailing-List: linux-doc@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 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? Cheers, Lance