Re: [PATCH] msi: Only keep one msi_desc in each slab entry.

[Eric W. Biederman]

"Pekka Enberg" <penberg@xxxxxxxxxxxxxx> writes:

> On 7/11/06, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>>
>> It looks like someone confused kmem_cache_create with a different
>> allocator and was attempting to give it knowledge of how many cache
>> entries there were.
>>
>> With the unfortunate result that each slab entry was big enough to
>> hold every irq.
>>
>> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
>> ---
>>  drivers/pci/msi.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index 0cd4a3e..082e942 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -40,13 +40,13 @@ msi_register(struct msi_ops *ops)
>>
>> static void msi_cache_ctor(void *p, kmem_cache_t *cache, unsigned long flags)
>>  {
>> -       memset(p, 0, NR_IRQS * sizeof(struct msi_desc));
>> +       memset(p, 0, sizeof(struct msi_desc));
>
> You can use kmem_cache_zalloc() for this.

Please look at what the code changes.
Please recognize how very bad the current code is behaving.

As for the rest sure go ahead and create a patch to address it
but that really is a separate issue and thus a separate patch.

I'm just trying to keep the kernel from calling BUG_ON the first
time a msi irq is allocated on a kernel with a maximum NR_CPUS
configuration, and from wasting memory the rest of the time.

Or you know how bad the msi code is when every patch to fix a major
issue is followed up comments on how to improve the code even further.

Eric

>>  }
>>
>>  static int msi_cache_init(void)
>>  {
>>         msi_cachep = kmem_cache_create("msi_cache",
>> -                       NR_IRQS * sizeof(struct msi_desc),
>> +                       sizeof(struct msi_desc),
>>                         0, SLAB_HWCACHE_ALIGN, msi_cache_ctor, NULL);
>>         if (!msi_cachep)
>>                 return -ENOMEM;
>> --
>> 1.4.1.gac83a
>>
>> -
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