linux-kernel - Re: [PATCH] lightnvm: limit get chunk meta request size

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Message-ID: <FA6B99A4-5CDA-4F43-81B1-F05303F63EC1@cnexlabs.com>
Date:   Thu, 5 Jul 2018 07:14:38 +0000
From:   Javier Gonzalez <javier@...xlabs.com>
To:     Matias Bjørling <mb@...htnvm.io>
CC:     "Konopko, Igor J" <igor.j.konopko@...el.com>,
        Marcin Dziegielewski <marcin.dziegielewski@...el.com>,
        Hans Holmberg <hans.holmberg@...xlabs.com>,
        Heiner Litz <hlitz@...c.edu>,
        Young Tack Tack Jin <youngtack.jin@...cuitblvd.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lightnvm: limit get chunk meta request size

> On 3 Jul 2018, at 21.14, Matias Bjørling <mb@...htnvm.io> wrote:
> 
> On 07/03/2018 09:10 PM, Javier Gonzalez wrote:
>>> On 2 Jul 2018, at 10.02, Matias Bjørling <mb@...htnvm.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@...htnvm.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@...xlabs.com>
> 
> I changed the title. Since it didn't touch pblk. Thanks.

Makes sense. Thanks!


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