Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Ming Lin]

On Thu, Apr 7, 2016 at 9:43 AM, Ming Lin  wrote:
> On Thu, Apr 7, 2016 at 7:56 AM, Bart Van Assche
>  wrote:
>> On 03/15/16 15:39, Ming Lin wrote:
>>>
>>> +static void sg_mempoll_free(struct scatterlist *sgl, unsigned int nents)
>>
>>
>> Please change mempoll into mempool.
>
> Good catch. Thanks Bart!

Hi Bart,

This is actually the previous old RFC patch.
The v2 and v3 patch series doesn't have this typo.

Thanks.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Ming Lin]

On Thu, Apr 7, 2016 at 9:43 AM, Ming Lin  wrote:
> On Thu, Apr 7, 2016 at 7:56 AM, Bart Van Assche
>  wrote:
>> On 03/15/16 15:39, Ming Lin wrote:
>>>
>>> +static void sg_mempoll_free(struct scatterlist *sgl, unsigned int nents)
>>
>>
>> Please change mempoll into mempool.
>
> Good catch. Thanks Bart!

Hi Bart,

This is actually the previous old RFC patch.
The v2 and v3 patch series doesn't have this typo.

Thanks.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Ming Lin]

On Thu, Apr 7, 2016 at 7:56 AM, Bart Van Assche
 wrote:
> On 03/15/16 15:39, Ming Lin wrote:
>>
>> +static void sg_mempoll_free(struct scatterlist *sgl, unsigned int nents)
>
>
> Please change mempoll into mempool.

Good catch. Thanks Bart!

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Ming Lin]

On Thu, Apr 7, 2016 at 7:56 AM, Bart Van Assche
 wrote:
> On 03/15/16 15:39, Ming Lin wrote:
>>
>> +static void sg_mempoll_free(struct scatterlist *sgl, unsigned int nents)
>
>
> Please change mempoll into mempool.

Good catch. Thanks Bart!

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Bart Van Assche]

On 03/15/16 15:39, Ming Lin wrote:

+static void sg_mempoll_free(struct scatterlist *sgl, unsigned int nents)


Please change mempoll into mempool.

Thanks,

Bart.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Bart Van Assche]

On 03/15/16 15:39, Ming Lin wrote:

+static void sg_mempoll_free(struct scatterlist *sgl, unsigned int nents)


Please change mempoll into mempool.

Thanks,

Bart.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Christoph Hellwig]

On Sun, Mar 20, 2016 at 11:55:17PM -0700, Ming Lin wrote:
> On Wed, 2016-03-16 at 09:23 +0100, Christoph Hellwig wrote:
> > > 
> > We can defintively kill this one.
> 
> We want to support different size of pools.
> How can we kill this one?
> 
> Or did you mean we just create a single pool with size SG_CHUNK_SIZE?

I mean just killing the SG_MEMPOOL_NR define and using the ARRAY_SIZE
directly.

> I created lib/sg_pool.c with CONFIG_SG_POOL.

Great!

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Christoph Hellwig]

On Sun, Mar 20, 2016 at 11:55:17PM -0700, Ming Lin wrote:
> On Wed, 2016-03-16 at 09:23 +0100, Christoph Hellwig wrote:
> > > 
> > We can defintively kill this one.
> 
> We want to support different size of pools.
> How can we kill this one?
> 
> Or did you mean we just create a single pool with size SG_CHUNK_SIZE?

I mean just killing the SG_MEMPOOL_NR define and using the ARRAY_SIZE
directly.

> I created lib/sg_pool.c with CONFIG_SG_POOL.

Great!

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Ming Lin]

On Wed, 2016-03-16 at 09:23 +0100, Christoph Hellwig wrote:
> > 
> We can defintively kill this one.

We want to support different size of pools.
How can we kill this one?

Or did you mean we just create a single pool with size SG_CHUNK_SIZE?

> 
> > +static __init int sg_mempool_init(void)
> > +{
> > +   int i;
> > +
> > +   for (i = 0; i < SG_MEMPOOL_NR; i++) {
> > +   struct sg_mempool *sgp = sg_pools + i;
> > +   int size = sgp->size * sizeof(struct scatterlist);
> > +
> > +   sgp->slab = kmem_cache_create(sgp->name, size, 0,
> > +   SLAB_HWCACHE_ALIGN, NULL);
> 
> Having these mempoools around in every kernel will make some embedded
> developers rather unhappy.  We could either not create them at
> runtime, which would require either a check in the fast path, or
> an init call in every driver, or just move the functions you
> added into a separe file, which will be compiled only based on a
> Kconfig
> symbol, and could even be potentially modular.  I think that
> second option might be easier.

I created lib/sg_pool.c with CONFIG_SG_POOL.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Ming Lin]

On Wed, 2016-03-16 at 09:23 +0100, Christoph Hellwig wrote:
> > 
> We can defintively kill this one.

We want to support different size of pools.
How can we kill this one?

Or did you mean we just create a single pool with size SG_CHUNK_SIZE?

> 
> > +static __init int sg_mempool_init(void)
> > +{
> > +   int i;
> > +
> > +   for (i = 0; i < SG_MEMPOOL_NR; i++) {
> > +   struct sg_mempool *sgp = sg_pools + i;
> > +   int size = sgp->size * sizeof(struct scatterlist);
> > +
> > +   sgp->slab = kmem_cache_create(sgp->name, size, 0,
> > +   SLAB_HWCACHE_ALIGN, NULL);
> 
> Having these mempoools around in every kernel will make some embedded
> developers rather unhappy.  We could either not create them at
> runtime, which would require either a check in the fast path, or
> an init call in every driver, or just move the functions you
> added into a separe file, which will be compiled only based on a
> Kconfig
> symbol, and could even be potentially modular.  I think that
> second option might be easier.

I created lib/sg_pool.c with CONFIG_SG_POOL.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Christoph Hellwig]

>  /*
> + * The maximum number of SG segments that we will put inside a
> + * scatterlist.
> + *
> + * XXX: what's the best number?
> + */
> +#define SG_MAX_SEGMENTS  128

The important part here is that it's the amount we fit into a single
scatterlist chunk.  So I think naming it SG_CHUNK_SIZE  or similar
would be a better idea (the name in SCSI is from the days before
we supported chained S/G lists).

It would also be good to ⅺring over the comments from
SCSI_MAX_SG_SEGMENTS.

We'll also need a symbol like SCSI_MAX_SG_CHAIN_SEGMENTS that contains
the absolute limit, and we need the CONFIG_ARCH_HAS_SG_CHAIN magic
around it for now as we still have architetures that do not support
S/G chanining in their dma_map_sg implementation.  I plan to fix that
up in a merge window or two, though.  My name suggestion for that
would be SG_MAX_SEGMENTS.

> +#define SG_MEMPOOL_NRARRAY_SIZE(sg_pools)

We can defintively kill this one.

> +#define SG_MEMPOOL_SIZE  2
> +
> +struct sg_mempool {

I'd keep this as struct sg_pool, similar to SCSI.

> +/**
> + * sg_free_chained - Free a previously mapped sg table
> + * @table:   The sg table header to use
> + * @first_chunk: was first_chunk not NULL in sg_alloc_chained?
> + *
> + *  Description:
> + *Free an sg table previously allocated and setup with
> + *sg_alloc_chained().
> + *
> + **/
> +void sg_free_chained(struct sg_table *table, bool first_chunk)

Can we call this sg_free_table_chained to be similar to sg_table_free?
Same for the alloc side.

> +static __init int sg_mempool_init(void)
> +{
> + int i;
> +
> + for (i = 0; i < SG_MEMPOOL_NR; i++) {
> + struct sg_mempool *sgp = sg_pools + i;
> + int size = sgp->size * sizeof(struct scatterlist);
> +
> + sgp->slab = kmem_cache_create(sgp->name, size, 0,
> + SLAB_HWCACHE_ALIGN, NULL);

Having these mempoools around in every kernel will make some embedded
developers rather unhappy.  We could either not create them at
runtime, which would require either a check in the fast path, or
an init call in every driver, or just move the functions you
added into a separe file, which will be compiled only based on a Kconfig
symbol, and could even be potentially modular.  I think that
second option might be easier.

Re: [PATCH RFC 1/2] scatterlist: add mempool based chained SG alloc/free api

[Christoph Hellwig]

>  /*
> + * The maximum number of SG segments that we will put inside a
> + * scatterlist.
> + *
> + * XXX: what's the best number?
> + */
> +#define SG_MAX_SEGMENTS  128

The important part here is that it's the amount we fit into a single
scatterlist chunk.  So I think naming it SG_CHUNK_SIZE  or similar
would be a better idea (the name in SCSI is from the days before
we supported chained S/G lists).

It would also be good to ⅺring over the comments from
SCSI_MAX_SG_SEGMENTS.

We'll also need a symbol like SCSI_MAX_SG_CHAIN_SEGMENTS that contains
the absolute limit, and we need the CONFIG_ARCH_HAS_SG_CHAIN magic
around it for now as we still have architetures that do not support
S/G chanining in their dma_map_sg implementation.  I plan to fix that
up in a merge window or two, though.  My name suggestion for that
would be SG_MAX_SEGMENTS.

> +#define SG_MEMPOOL_NRARRAY_SIZE(sg_pools)

We can defintively kill this one.

> +#define SG_MEMPOOL_SIZE  2
> +
> +struct sg_mempool {

I'd keep this as struct sg_pool, similar to SCSI.

> +/**
> + * sg_free_chained - Free a previously mapped sg table
> + * @table:   The sg table header to use
> + * @first_chunk: was first_chunk not NULL in sg_alloc_chained?
> + *
> + *  Description:
> + *Free an sg table previously allocated and setup with
> + *sg_alloc_chained().
> + *
> + **/
> +void sg_free_chained(struct sg_table *table, bool first_chunk)

Can we call this sg_free_table_chained to be similar to sg_table_free?
Same for the alloc side.

> +static __init int sg_mempool_init(void)
> +{
> + int i;
> +
> + for (i = 0; i < SG_MEMPOOL_NR; i++) {
> + struct sg_mempool *sgp = sg_pools + i;
> + int size = sgp->size * sizeof(struct scatterlist);
> +
> + sgp->slab = kmem_cache_create(sgp->name, size, 0,
> + SLAB_HWCACHE_ALIGN, NULL);

Having these mempoools around in every kernel will make some embedded
developers rather unhappy.  We could either not create them at
runtime, which would require either a check in the fast path, or
an init call in every driver, or just move the functions you
added into a separe file, which will be compiled only based on a Kconfig
symbol, and could even be potentially modular.  I think that
second option might be easier.