From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> To: Will Deacon <will@kernel.org>, Robin Murphy <robin.murphy@arm.com> Cc: iommu <iommu@lists.linux-foundation.org>, linux-arm-kernel <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: remove unnecessary oom message Date: Wed, 16 Jun 2021 09:47:18 +0800 [thread overview] Message-ID: <c94b7ba9-b85b-4704-6335-17334bc56f1b@huawei.com> (raw) In-Reply-To: <20210615115507.GD20598@willie-the-truck> On 2021/6/15 19:55, Will Deacon wrote: > On Tue, Jun 15, 2021 at 12:51:38PM +0100, Robin Murphy wrote: >> On 2021-06-15 12:34, Will Deacon wrote: >>> 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. >> >> Agreed - other than deliberately-contrived situations I don't think I've >> ever hit a genuine OOM, but I definitely have debugged attempts to allocate >> -1 of something. If the driver-specific message actually calls out the >> critical information, e.g. "failed to allocate %d stream table entries", it >> gives debugging a head start since the miscalculation is obvious, but a >> static message that only identifies the callsite really only saves a quick >> trip to scripts/faddr2line, and personally I've never found that >> particularly valuable. > > So it sounds like this particular patch is fine, but the one for smmuv2 > should leave the IRQ allocation message alone (by virtue of it printing > something a bit more useful -- the number of irqs). num_irqs = 0; while ((res = platform_get_resource(pdev, IORESOURCE_IRQ, num_irqs))) { num_irqs++; } As the above code, num_irqs is calculated based on the number of dtb or acpi configuration items, it can't be too large. That is, there is almost zero chance that devm_kcalloc() will fail because num_irqs is too large. > > Will > > . > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
WARNING: multiple messages have this Message-ID (diff)
From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> To: Will Deacon <will@kernel.org>, Robin Murphy <robin.murphy@arm.com> Cc: linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, Joerg Roedel <joro@8bytes.org>, iommu <iommu@lists.linux-foundation.org> Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: remove unnecessary oom message Date: Wed, 16 Jun 2021 09:47:18 +0800 [thread overview] Message-ID: <c94b7ba9-b85b-4704-6335-17334bc56f1b@huawei.com> (raw) In-Reply-To: <20210615115507.GD20598@willie-the-truck> On 2021/6/15 19:55, Will Deacon wrote: > On Tue, Jun 15, 2021 at 12:51:38PM +0100, Robin Murphy wrote: >> On 2021-06-15 12:34, Will Deacon wrote: >>> 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. >> >> Agreed - other than deliberately-contrived situations I don't think I've >> ever hit a genuine OOM, but I definitely have debugged attempts to allocate >> -1 of something. If the driver-specific message actually calls out the >> critical information, e.g. "failed to allocate %d stream table entries", it >> gives debugging a head start since the miscalculation is obvious, but a >> static message that only identifies the callsite really only saves a quick >> trip to scripts/faddr2line, and personally I've never found that >> particularly valuable. > > So it sounds like this particular patch is fine, but the one for smmuv2 > should leave the IRQ allocation message alone (by virtue of it printing > something a bit more useful -- the number of irqs). num_irqs = 0; while ((res = platform_get_resource(pdev, IORESOURCE_IRQ, num_irqs))) { num_irqs++; } As the above code, num_irqs is calculated based on the number of dtb or acpi configuration items, it can't be too large. That is, there is almost zero chance that devm_kcalloc() will fail because num_irqs is too large. > > Will > > . > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-06-16 1:47 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-09 12:54 [PATCH 1/1] iommu/arm-smmu-v3: remove unnecessary oom message Zhen Lei 2021-06-09 12:54 ` Zhen Lei 2021-06-11 10:32 ` Will Deacon 2021-06-11 10:32 ` Will Deacon 2021-06-15 11:22 ` Leizhen (ThunderTown) 2021-06-15 11:22 ` Leizhen (ThunderTown) 2021-06-15 11:34 ` Will Deacon 2021-06-15 11:34 ` Will Deacon 2021-06-15 11:36 ` Will Deacon 2021-06-15 11:36 ` Will Deacon 2021-06-15 11:51 ` Robin Murphy 2021-06-15 11:51 ` Robin Murphy 2021-06-15 11:55 ` Will Deacon 2021-06-15 11:55 ` Will Deacon 2021-06-16 1:47 ` Leizhen (ThunderTown) [this message] 2021-06-16 1:47 ` Leizhen (ThunderTown) 2021-06-16 10:10 ` Will Deacon 2021-06-16 10:10 ` Will Deacon 2021-06-15 19:18 ` Will Deacon 2021-06-15 19:18 ` Will Deacon
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