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Sat, 23 Jan 2021 08:01:37 +0000 Received: from BYAPR10MB2663.namprd10.prod.outlook.com ([fe80::644d:92e4:7b5d:f8c1]) by BYAPR10MB2663.namprd10.prod.outlook.com ([fe80::644d:92e4:7b5d:f8c1%5]) with mapi id 15.20.3784.016; Sat, 23 Jan 2021 08:01:37 +0000 Subject: Re: [PATCH 1/1] vhost scsi: allocate vhost_scsi with GFP_NOWAIT to avoid delay To: Jason Wang , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, mst@redhat.com, pbonzini@redhat.com, stefanha@redhat.com, joe.jin@oracle.com, aruna.ramakrishna@oracle.com References: <20210121050328.7891-1-dongli.zhang@oracle.com> <3aa5c6ca-abd3-13c4-b6a6-504f3a52bae7@redhat.com> From: Dongli Zhang Message-ID: <5a03abaf-cbd6-242c-c965-b2da577da816@oracle.com> Date: Sat, 23 Jan 2021 00:01:51 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 In-Reply-To: <3aa5c6ca-abd3-13c4-b6a6-504f3a52bae7@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [2601:646:c303:6700::a4a4] X-ClientProxiedBy: CH2PR14CA0053.namprd14.prod.outlook.com (2603:10b6:610:56::33) To BYAPR10MB2663.namprd10.prod.outlook.com (2603:10b6:a02:a9::20) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2601:646:c303:6700::a4a4] (2601:646:c303:6700::a4a4) by CH2PR14CA0053.namprd14.prod.outlook.com (2603:10b6:610:56::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3784.12 via Frontend Transport; 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It may take long time >> delay by kzalloc() to compact memory pages when there is a lack of >> high-order pages. As a result, there is latency to create a VM (with >> vhost-scsi) or to hotadd vhost-scsi-based storage. >> >> The prior commit 595cb754983d ("vhost/scsi: use vmalloc for order-10 >> allocation") prefers to fallback only when really needed, while this patch >> changes allocation to GFP_NOWAIT in order to avoid the delay caused by >> memory page compact. >> >> Cc: Aruna Ramakrishna >> Cc: Joe Jin >> Signed-off-by: Dongli Zhang >> --- >> Another option is to rework by reducing the size of 'struct vhost_scsi', >> e.g., by replacing inline vhost_scsi.vqs with just memory pointers while >> each vhost_scsi.vqs[i] should be allocated separately. Please let me >> know if that option is better. >> >>   drivers/vhost/scsi.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c >> index 4ce9f00ae10e..85eaa4e883f4 100644 >> --- a/drivers/vhost/scsi.c >> +++ b/drivers/vhost/scsi.c >> @@ -1814,7 +1814,7 @@ static int vhost_scsi_open(struct inode *inode, struct >> file *f) >>       struct vhost_virtqueue **vqs; >>       int r = -ENOMEM, i; >>   -    vs = kzalloc(sizeof(*vs), GFP_KERNEL | __GFP_NOWARN | >> __GFP_RETRY_MAYFAIL); >> +    vs = kzalloc(sizeof(*vs), GFP_NOWAIT | __GFP_NOWARN); >>       if (!vs) { >>           vs = vzalloc(sizeof(*vs)); >>           if (!vs) > > > Can we use kvzalloc? > Thank you very much for the suggestion. To use 'GFP_NOWAIT' will avoid any direct compact in __alloc_pages_slowpath(), while to use kvzalloc() will just avoid retrying direct compact for multiple times. Although the latter will still do direct compact (without retry), I think it is better than the former using GFP_NOWAIT. I will send v2 with kvzalloc(). Thank you very much! Dongli Zhang