Simple example of using slab allocator?

Simple example of using slab allocator?

Post by Andreas Dilge » Wed, 20 Jun 2001 02:00:10



Quote:Matthew Dharm writes:
> For 2.5, I'm planning on switching my driver over to the slab allocator,
> for a variety of reasons.  Does anyone have a _dead_ simple example of how
> to use such a beast?  I've seen the various web pages and document
> explaining the API, but I love to see working examples for reference (and
> to fill in the blanks).

The slab allocator IS dead simple to use, basically:

- driver global variable:

kmem_cache_t *usb_mass_cachep;

- in the driver init function:

        usb_mass_cachep = kmem_cache_create("usb_mass_cache",
                                            sizeof(struct whatever),
                                            0, SLAB_HWCACHE_ALIGN,
                                            NULL, NULL);
        (check for NULL usb_mass_slab)

- in the driver cleanup function:

        if (usb_mass_cachep && kmem_cache_destroy(usb_mass_cachep))
                printk(KERN_ERR "usb_mass_cache: not all structures freed\n");

- wherever you need an item from the slab cache:

        whateverp = kmem_cache_alloc(usb_mass_cachep, GFP_KERNEL);
        (check for NULL whateverp)

- when you are done with it:

        kmem_cache_free(usb_mass_cachep, whateverp);

Notes:
- if you have a slab leak and you don't free all of the items (hence the slab
  cache is not removed), you will probably get an oops when you reload the
  driver.  You can only have one slab cache per name ("usb_mass_cache" here).
- You may need different alignment (SLAB_HWCACHE_ALIGN), or not
- You may need different allocation policy (GFP_KERNEL), or not

Cheers, Andreas
--
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert
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Simple example of using slab allocator?

Post by Matthew Dhar » Wed, 20 Jun 2001 15:20:06


Well, if it's really that simple....

Another aspect of this, tho, is that I'd like to be able to profile my
memory usage.  Does the SA have any ability to report (easily) the number
of pages allocated and how full each one is?

Matt Dharm


> Matthew Dharm writes:
> > For 2.5, I'm planning on switching my driver over to the slab allocator,
> > for a variety of reasons.  Does anyone have a _dead_ simple example of how
> > to use such a beast?  I've seen the various web pages and document
> > explaining the API, but I love to see working examples for reference (and
> > to fill in the blanks).

> The slab allocator IS dead simple to use, basically:

> - driver global variable:

> kmem_cache_t *usb_mass_cachep;

> - in the driver init function:

>    usb_mass_cachep = kmem_cache_create("usb_mass_cache",
>                                        sizeof(struct whatever),
>                                        0, SLAB_HWCACHE_ALIGN,
>                                        NULL, NULL);
>    (check for NULL usb_mass_slab)

> - in the driver cleanup function:

>    if (usb_mass_cachep && kmem_cache_destroy(usb_mass_cachep))
>            printk(KERN_ERR "usb_mass_cache: not all structures freed\n");

> - wherever you need an item from the slab cache:

>    whateverp = kmem_cache_alloc(usb_mass_cachep, GFP_KERNEL);
>    (check for NULL whateverp)

> - when you are done with it:

>    kmem_cache_free(usb_mass_cachep, whateverp);

> Notes:
> - if you have a slab leak and you don't free all of the items (hence the slab
>   cache is not removed), you will probably get an oops when you reload the
>   driver.  You can only have one slab cache per name ("usb_mass_cache" here).
> - You may need different alignment (SLAB_HWCACHE_ALIGN), or not
> - You may need different allocation policy (GFP_KERNEL), or not

> Cheers, Andreas
> --
> Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
>                  \  would they cancel out, leaving him still hungry?"
> http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert

--

Maintainer, Linux USB Mass Storage Driver

God, root, what is difference?
                                        -- Pitr
User Friendly, 11/11/1999

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Simple example of using slab allocator?

Post by Andreas Dilge » Wed, 20 Jun 2001 17:00:13


Quote:Matthew Dharm writes:
> Well, if it's really that simple....

> Another aspect of this, tho, is that I'd like to be able to profile my
> memory usage.  Does the SA have any ability to report (easily) the number
> of pages allocated and how full each one is?

Then "cat /proc/slabinfo" is your friend.  It lists currently allocated
objects, maximum objects that will fit in the current allocated pages,
size of object, pages used if objects were tightly packed, real pages
used, and pages per slab.

On SMP systems it also lists the number of slab cache objects kept
local to each CPU to avoid global locking when they need to allocate.

Cheers, Andreas


> > The slab allocator IS dead simple to use, basically:

> > - driver global variable:

> > kmem_cache_t *usb_mass_cachep;

> > - in the driver init function:

> >       usb_mass_cachep = kmem_cache_create("usb_mass_cache",
> >                                           sizeof(struct whatever),
> >                                           0, SLAB_HWCACHE_ALIGN,
> >                                           NULL, NULL);
> >       (check for NULL usb_mass_slab)

> > - in the driver cleanup function:

> >       if (usb_mass_cachep && kmem_cache_destroy(usb_mass_cachep))
> >               printk(KERN_ERR "usb_mass_cache: not all structures freed\n");

> > - wherever you need an item from the slab cache:

> >       whateverp = kmem_cache_alloc(usb_mass_cachep, GFP_KERNEL);
> >       (check for NULL whateverp)

> > - when you are done with it:

> >       kmem_cache_free(usb_mass_cachep, whateverp);

> > Notes:
> > - if you have a slab leak and you don't free all of the items (hence the slab
> >   cache is not removed), you will probably get an oops when you reload the
> >   driver.  You can only have one slab cache per name ("usb_mass_cache" here).
> > - You may need different alignment (SLAB_HWCACHE_ALIGN), or not
> > - You may need different allocation policy (GFP_KERNEL), or not

--
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert
-
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Please read the FAQ at  http://www.tux.org/lkml/