From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CED6CC79FBD for ; Wed, 9 Sep 2026 16:01:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CF8A96B00A7; Wed, 9 Sep 2026 12:01:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CD0656B00A9; Wed, 9 Sep 2026 12:01:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BE5D86B00AA; Wed, 9 Sep 2026 12:01:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 837E96B00A7 for ; Wed, 9 Sep 2026 12:01:03 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id DC2C68026F for ; Wed, 9 Sep 2026 16:01:02 +0000 (UTC) X-FDA: 85194687564.12.7156A67 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by imf14.hostedemail.com (Postfix) with ESMTP id 4BA17100013 for ; Wed, 9 Sep 2026 16:01:00 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=TCRP94SY; spf=pass (imf14.hostedemail.com: domain of rnsastry@linux.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=rnsastry@linux.ibm.com; dmarc=pass (policy=none) header.from=ibm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788969660; h=from:from:sender: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:dkim-signature; bh=00JU/j/v+DQy0zd7AxUZ9dWcvelnFmS2j8kJVfQrbIQ=; b=CcVDz6BZuoq3Z/j48/hNUh7lBqXOObFvTmMJjR8Ss8/hMFwEblFVhGclu852m/tY9bjQa6 LdvWRCWTMdSaOTHjkWkPrGOOh6ZP+63mBvFVdNvkgF0I2xErbheqsrw1jmC6ArvbJyd5Ja 7XDN4tqPXsuvleNGequsjxfDpLLbbEs= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=TCRP94SY; spf=pass (imf14.hostedemail.com: domain of rnsastry@linux.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=rnsastry@linux.ibm.com; dmarc=pass (policy=none) header.from=ibm.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788969660; b=PQUL1qEWKyANRZNWkvUNhR2+pEVLGwrSzyTgeGwdUP3PmEEmbvT+TxNKn3DjacFeWwtmGx J7WsVml0BBn7udUepcXFUhJ37X2Hu7R91tBvqi9/WaEl13M0oFua5dJNtw32B1NdwJ9S88 ZLge7L+QrxqOBec8oH7mURkeg2eSWZM= Received: from pps.filterd (m0360083.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 689B1RXR3817363; Wed, 9 Sep 2026 16:00:49 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=00JU/j /v+DQy0zd7AxUZ9dWcvelnFmS2j8kJVfQrbIQ=; b=TCRP94SY0JQW+S+PR540yU u/lnGUruItr+yZJ8X2SS9trYAqJ5WEcHubrqfQjfVHOhb8tVlMTk1YiNZHOyWMQZ Fp/90cFh4QWFO6uSqV8YSFTGD4nlRRLPlL3Fh2NLOMFzNK9zNXZcu7EQ1yJY0O2f p9RnrmEihlwh4ZzfrFyPCw1Skf2yfri9pRZb5qYGP1b+yeeM9A3K6a/3Y0Bry9re G1dP/e8+Smt9Zvmv5itpSwDcz3kNGNNUK1GkSx00YAnG+MHFjfPeJIVH/iJ76zIH m8keWUtjRQwuhs2Bx+ITGBT0CbU8jYF5uD7lWfhMHN/WYUeqGm2vEBQLa8vr6Zkg == Received: from ppma11.dal12v.mail.ibm.com (db.9e.1632.ip4.static.sl-reverse.com [50.22.158.219]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4ggbf46y64-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 09 Sep 2026 16:00:48 +0000 (GMT) Received: from pps.filterd (ppma11.dal12v.mail.ibm.com [127.0.0.1]) by ppma11.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 689FuLt0015882; Wed, 9 Sep 2026 16:00:47 GMT Received: from smtprelay03.fra02v.mail.ibm.com ([9.218.2.224]) by ppma11.dal12v.mail.ibm.com (PPS) with ESMTPS id 4gh03yjy97-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 09 Sep 2026 16:00:47 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 689G0jcA35717428 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 9 Sep 2026 16:00:45 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E333B2004D; Wed, 9 Sep 2026 16:00:44 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2CA3C20040; Wed, 9 Sep 2026 16:00:35 +0000 (GMT) Received: from [9.61.255.18] (unknown [9.61.255.18]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 9 Sep 2026 16:00:34 +0000 (GMT) Message-ID: <96f4e19c-26d6-481c-b7b3-0a2aa244c834@linux.ibm.com> Date: Wed, 9 Sep 2026 21:30:31 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 11/22] coredump: always chunk writes To: Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Jacob Lalonde , Josef Bacik , Jann Horn , Alexander Viro , Jan Kara , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Omar Sandoval , Jacob Lalonde , Shuah Khan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <20260820-work-coredump-sparse-v2-0-ba32dd718c51@kernel.org> <20260820-work-coredump-sparse-v2-11-ba32dd718c51@kernel.org> Content-Language: en-US From: R Nageswara Sastry In-Reply-To: <20260820-work-coredump-sparse-v2-11-ba32dd718c51@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: 3nsD3dyD9YpDNwrNy79mh4k3ZJgZAoAH X-Proofpoint-GUID: 5Ftz_v8DnqJwrQicAaxaxCLwd-1LE4ML X-Authority-Analysis: v=2.4 cv=DbEnbPtW c=1 sm=1 tr=0 ts=6aa182b0 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=uNwIYxRw8H9XJLvQjW8A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA5MDE3MyBTYWx0ZWRfX63FEwKXn2pEz lbN9cHVZiZXHc6txdAexnXMJtgrSfc5kgQl/RQL8aZJ3oiw7NqTF/WCwpFMjKmwq5NLNAZGgf7Q Hos7o2aQf/uCGOISPuipeIO0MunRkNE9zvUd5wusnjKNruB11Hx/j+gFzlJp3hJieicpYa+eeNs VkPI2SMmIPn7I8IL8WFtQVjvsWoy1UeU+NFUVDQ9KSshErJfbe9cDG4v706+PSGMOWzSjuy2imC 9rWzGxzVCn+WakqwhrsdV1oF+VDabMe2ZSGc8J+rU+SeWGZOzqQ4nHzexEQxcNU7ZreEcsXHjqT vnXmtYO1/SidK4tC78nZhlCXtSFAnu9ZuG6T+KEDlEJGJ1VsWRB5SVXl0be+AWY/znuXep8HXml ttmhJajuNA1n59oxzUkxRDb3KE0j9eapA5s1nPeKFV5w3rVkfbJFceEiLji4I9KbtpKV+mI6BiC 6wZ/lWkQABb3bef66Dw== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA5MDE3MyBTYWx0ZWRfXxpDMqZtbveKw EOHJ1ijEo1wcbWvww4tsJatXr/zaCikRtHGXSA8SYhI/DW4OjGh4H87T7udcjzwwogzipPCpPGc TkIi4XOACd8bpzimfR/h+x2eYMoJeMY= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-08_03,2026-09-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 impostorscore=0 adultscore=0 spamscore=0 clxscore=1015 suspectscore=0 bulkscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609090173 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4BA17100013 X-Stat-Signature: 6ags46hkx4a45mo1fqqtxwn33iuz4ac7 X-Rspam-User: X-HE-Tag: 1788969660-663555 X-HE-Meta: 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 WvpqqLrY 5iN/RmZAIb2kPXTtnW4iPOxJAodzHOpoDFU4C5/CD2VvyE7aNhC9asdzOouXeeFyMYlQqwZU1GtN95F5Qc+KRtDuywimCbHvv5YEIqhO7+9Qut/7ZQ1ZYzQT79ZhkGZdUNB1bx3oC1PBt4nioOKzESQ71l8WqgT7a9VAI2E314g1PMu5ogP4Rt6eKdZMfd6zA2fmIByGn4z5X1nU1U9HlDyYIDKpYHzM1GsdsCINXL0URFU21qesDUbHeRoEN+Y2prWhK/9ze5oyUnyuWfYH/PhYPvWbiQyikR1X8VHW7I7gWK76dkcVic1o2TUGvjYdAoEJ5v07dTPT8IS13KGkwtC3v4YMFpwMDH8L+eNZJZdFQirl0Gz0HWr11Kg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 20.08.2026 4:39 AM, Christian Brauner wrote: > Right now dump_emit() is the only coredump helper that writes buffers > larger than a page in one call. For elf notes that can easily blow past > PAGE_SIZE. That's annoying because neither pipes nor af_unix sockets > take such writes in one piece. > > If a signal arrives while the writer is waiting they drop a short write. > With the coredump records work coming up that means header and its data > are desynchronized. A write that fits in one pipe buffer or one skb > doesn't suffer from this. > > So split all writes up, including elf notes, and cap every write at a > page. The coredump socket already raises sk_sndbuf far enough for a page > to fit a single skb and pipes always work that way. > > That means dump_interrupted() is now checked once per page. So a large > coredump stops earlier (good). An empty write no longer issues a > zero-length write. The rlimit core check stays where it was. It > continues refusing whole writes. > > Signed-off-by: Christian Brauner (Amutable) Tested-by: R Nageswara Sastry System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2 > --- > fs/coredump.c | 37 ++++++++++++++++++++++++++++++------- > 1 file changed, 30 insertions(+), 7 deletions(-) > > diff --git a/fs/coredump.c b/fs/coredump.c > index d837819031ff..d61f36239f91 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -1215,19 +1215,21 @@ void vfs_coredump(const kernel_siginfo_t *siginfo) > * do on a core-file: use only these functions to write out all the > * necessary info. > */ > -static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) > +/* One write, never more than a page. See __dump_emit(). */ > +static bool dump_emit_chunk(struct coredump_params *cprm, const void *addr, > + int nr) > { > struct file *file = cprm->file; > loff_t pos = file->f_pos; > ssize_t n; > > - if (cprm->written + nr > cprm->limit) > - return false; > if (dump_interrupted()) > return false; > + > n = __kernel_write(file, addr, nr, &pos); > if (n != nr) > return false; > + > file->f_pos = pos; > cprm->written += n; > cprm->pos += n; > @@ -1235,6 +1237,24 @@ static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) > return true; > } > > +static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) > +{ > + if (cprm->written + nr > cprm->limit) > + return false; > + > + while (nr) { > + int chunk = min_t(int, nr, PAGE_SIZE); > + > + if (!dump_emit_chunk(cprm, addr, chunk)) > + return false; > + > + addr += chunk; > + nr -= chunk; > + } > + > + return true; > +} > + > static bool __dump_skip(struct coredump_params *cprm, size_t nr) > { > static char zeroes[PAGE_SIZE]; > @@ -1247,13 +1267,16 @@ static bool __dump_skip(struct coredump_params *cprm, size_t nr) > return true; > } > > - while (nr > PAGE_SIZE) { > - if (!__dump_emit(cprm, zeroes, PAGE_SIZE)) > + while (nr) { > + size_t chunk = min_t(size_t, nr, PAGE_SIZE); > + > + if (!__dump_emit(cprm, zeroes, chunk)) > return false; > - nr -= PAGE_SIZE; > + > + nr -= chunk; > } > > - return __dump_emit(cprm, zeroes, nr); > + return true; > } > > /* Flush the accumulated hole before writing data. */ > -- Thanks and Regards R.Nageswara Sastry