From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (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 369972F5A3B for ; Tue, 2 Dec 2025 04:50:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764651026; cv=none; b=VU4nhRa+9tR/4DxTXcVFqyJGJ2et0H/8W2rnyCBj/Hh8ZjqNwjSIzvznM7Hn2rW52aMMhBOG9d6ls0Z/4KwJqHAh9/OsLh7PYx1s22v17xF+Ca79bNm8+TmM+DjOaTki35LJFMwWApetOUoR6f3TeZEzDNlV16XjgoWkMcWIUfE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764651026; c=relaxed/simple; bh=k4H9fK6qG3Sv9HHzmLZL0QomcRdBJMDXXDfhZROR2cY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=e1GWI08jE1PItCJRRxKBL422iyjND+NvpWtZakT72oaw0KqmlUOZ6ShZaXgKLsulFt3tJrOCFzy3eLhpWsP+J0EvD/l3h5cekPBkTSXhbXZ4UfhxT9q5j5YGweP3VTIwBJh9X7JtUOCUo7M2RDM/uIYJRAdGVZwHkWpmFzacnOA= 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=Vhf4fPTv; arc=none smtp.client-ip=91.218.175.184 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="Vhf4fPTv" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1764651021; 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=jGcwHsaLozazj4k3fLuhDAgiJq4CZqWj7W2bZnDVz00=; b=Vhf4fPTv9xrM0TVReTjEl9+EMYLp0tEVePWzanveohCdmTef90eIKFHknogXNKZ6Le/z0o I61Y4XwSd4fu3+0t7bqLxX3HSqN+jT8VusYx/USEQ34m668NGVbuciyZShZdeDO+u2yYS+ H1D/xZ5EkUmxb/QqNVzS6uP7R+KOe2U= Date: Tue, 2 Dec 2025 12:50:04 +0800 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH V3 2/2] mm/khugepaged: retry with sync writeback for MADV_COLLAPSE To: Shivank Garg Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Andrew Morton , Ryan Roberts , Dev Jain , Lorenzo Stoakes , Barry Song , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Zach O'Keefe , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Branden Moore References: <20251201185604.210634-6-shivankg@amd.com> <20251201185604.210634-10-shivankg@amd.com> 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: <20251201185604.210634-10-shivankg@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/12/2 02:56, Shivank Garg wrote: > When MADV_COLLAPSE is called on file-backed mappings (e.g., executable > text sections), the pages may still be dirty from recent writes. > collapse_file() will trigger async writeback and fail with > SCAN_PAGE_DIRTY_OR_WRITEBACK (-EAGAIN). > > MADV_COLLAPSE is a synchronous operation where userspace expects > immediate results. If the collapse fails due to dirty pages, perform > synchronous writeback on the specific range and retry once. > > This avoids spurious failures for freshly written executables while > avoiding unnecessary synchronous I/O for mappings that are already clean. > > Reported-by: Branden Moore > Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com > Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE") > Suggested-by: David Hildenbrand > Signed-off-by: Shivank Garg > --- > mm/khugepaged.c | 41 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 41 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 219dfa2e523c..7a12e9ef30b4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -22,6 +22,7 @@ > #include > #include > #include > +#include > > #include > #include "internal.h" > @@ -2787,9 +2788,11 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > hend = end & HPAGE_PMD_MASK; > > for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { > + bool retried = false; > int result = SCAN_FAIL; > > if (!mmap_locked) { > +retry: > cond_resched(); > mmap_read_lock(mm); > mmap_locked = true; > @@ -2819,6 +2822,44 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > if (!mmap_locked) > *lock_dropped = true; > > + /* > + * If the file-backed VMA has dirty pages, the scan triggers > + * async writeback and returns SCAN_PAGE_DIRTY_OR_WRITEBACK. > + * Since MADV_COLLAPSE is sync, we force sync writeback and > + * retry once. > + */ > + if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !retried) { > + /* > + * File scan drops the lock. We must re-acquire it to > + * safely inspect the VMA and hold the file reference. > + */ > + if (!mmap_locked) { > + cond_resched(); > + mmap_read_lock(mm); > + mmap_locked = true; > + result = hugepage_vma_revalidate(mm, addr, false, &vma, cc); > + if (result != SCAN_SUCCEED) > + goto handle_result; > + } > + > + if (!vma_is_anonymous(vma) && vma->vm_file && > + mapping_can_writeback(vma->vm_file->f_mapping)) { > + struct file *file = get_file(vma->vm_file); > + pgoff_t pgoff = linear_page_index(vma, addr); > + loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; > + loff_t lend = lstart + HPAGE_PMD_SIZE - 1; > + > + mmap_read_unlock(mm); > + mmap_locked = false; > + *lock_dropped = true; > + filemap_write_and_wait_range(file->f_mapping, lstart, lend); > + fput(file); > + retried = true; > + goto retry; > + } > + } > + > + Nit: spurious blank line. > handle_result: > switch (result) { > case SCAN_SUCCEED: