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Subject: Re: [PATCH] lightnvm: limit get chunk meta request size
To:     javier@cnexlabs.com
Cc:     igor.j.konopko@intel.com, marcin.dziegielewski@intel.com,
        hans.holmberg@cnexlabs.com, hlitz@ucsc.edu,
        youngtack.jin@circuitblvd.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20180702080223.13214-1-mb@lightnvm.io>
 <C0B26672-CFD1-4058-A979-48341CD40F8D@cnexlabs.com>
From:   =?UTF-8?Q?Matias_Bj=c3=b8rling?= <mb@lightnvm.io>
Message-ID: <dd3b8963-1f11-59a6-dc60-e0171687a727@lightnvm.io>
Date:   Tue, 3 Jul 2018 21:14:50 +0200
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On 07/03/2018 09:10 PM, Javier Gonzalez wrote:
>> On 2 Jul 2018, at 10.02, Matias Bjørling <mb@lightnvm.io> wrote:
>>
>> For devices that does not specify a limit on its transfer size, the
>> get_chk_meta command may send down a single I/O retrieving the full
>> chunk metadata table. Resulting in large 2-4MB I/O requests. Instead,
>> split up the I/Os to a maximum of 256KB and issue them separately to
>> reduce memory requirements.
>>
>> Signed-off-by: Matias Bjørling <mb@lightnvm.io>
>> ---
>> drivers/nvme/host/lightnvm.c | 10 ++++++++--
>> 1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/nvme/host/lightnvm.c b/drivers/nvme/host/lightnvm.c
>> index b9989717418d..3b644b0e9713 100644
>> --- a/drivers/nvme/host/lightnvm.c
>> +++ b/drivers/nvme/host/lightnvm.c
>> @@ -583,7 +583,13 @@ static int nvme_nvm_get_chk_meta(struct nvm_dev *ndev,
>> 	struct ppa_addr ppa;
>> 	size_t left = nchks * sizeof(struct nvme_nvm_chk_meta);
>> 	size_t log_pos, offset, len;
>> -	int ret, i;
>> +	int ret, i, max_len;
>> +
>> +	/*
>> +	 * limit requests to maximum 256K to avoid issuing arbitrary large
>> +	 * requests when the device does not specific a maximum transfer size.
>> +	 */
>> +	max_len = min_t(unsigned int, ctrl->max_hw_sectors << 9, 256 * 1024);
>>
>> 	/* Normalize lba address space to obtain log offset */
>> 	ppa.ppa = slba;
>> @@ -596,7 +602,7 @@ static int nvme_nvm_get_chk_meta(struct nvm_dev *ndev,
>> 	offset = log_pos * sizeof(struct nvme_nvm_chk_meta);
>>
>> 	while (left) {
>> -		len = min_t(unsigned int, left, ctrl->max_hw_sectors << 9);
>> +		len = min_t(unsigned int, left, max_len);
>>
>> 		ret = nvme_get_log_ext(ctrl, ns, NVME_NVM_LOG_REPORT_CHUNK,
>> 				dev_meta, len, offset);
>> --
>> 2.11.0
> 
> Is this a v2? I remember seeing this patch being posted before [1]. It
> still looks good to me :)
> 
> 
> [1] https://lkml.org/lkml/2018/6/12/466
> 
> 
> Reviewed-by: Javier González <javier@cnexlabs.com>
> 

I changed the title. Since it didn't touch pblk. Thanks.