Re: [PATCH 1/1] iommu/arm-smmu-v3: remove unnecessary oom message

[Will Deacon <will@kernel.org>]

On Tue, Jun 15, 2021 at 07:22:10PM +0800, Leizhen (ThunderTown) wrote:
> 
> 
> On 2021/6/11 18:32, Will Deacon wrote:
> > On Wed, Jun 09, 2021 at 08:54:38PM +0800, Zhen Lei wrote:
> >> Fixes scripts/checkpatch.pl warning:
> >> WARNING: Possible unnecessary 'out of memory' message
> >>
> >> Remove it can help us save a bit of memory.
> >>
> >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> >> ---
> >>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 ++------
> >>  1 file changed, 2 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >> index 2ddc3cd5a7d1..fd7c55b44881 100644
> >> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >> @@ -2787,10 +2787,8 @@ static int arm_smmu_init_l1_strtab(struct arm_smmu_device *smmu)
> >>  	void *strtab = smmu->strtab_cfg.strtab;
> >>  
> >>  	cfg->l1_desc = devm_kzalloc(smmu->dev, size, GFP_KERNEL);
> >> -	if (!cfg->l1_desc) {
> >> -		dev_err(smmu->dev, "failed to allocate l1 stream table desc\n");
> >> +	if (!cfg->l1_desc)
> > 
> > What error do you get if devm_kzalloc() fails? I'd like to make sure it's
> > easy to track down _which_ allocation failed in that case -- does it give
> > you a line number, for example?
> 
> When devm_kzalloc() fails, the OOM information is printed. No line number information, but the
> size(order) and call stack is printed. It doesn't matter which allocation failed, the failure
> is caused by insufficient system memory rather than the fault of the SMMU driver. Therefore,
> the current printing is not helpful for locating the problem of insufficient memory. After all,
> when memory allocation fails, the SMMU driver cannot work at a lower specification.

I don't entirely agree. Another reason for the failure is because the driver
might be asking for a huge (or negative) allocation, in which case it might
be instructive to have a look at the actual caller, particularly if the
size is derived from hardware or firmware properties.

Will

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