On Fri, Mar 29 2013, Glauber Costa wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> The current shrinker callout API uses an a single shrinker call for
> multiple functions. To determine the function, a special magical
> value is passed in a parameter to change the behaviour. This
> complicates the implementation and return value specification for
> the different behaviours.
>
> Separate the two different behaviours into separate operations, one
> to return a count of freeable objects in the cache, and another to
> scan a certain number of objects in the cache for freeing. In
> defining these new operations, ensure the return values and
> resultant behaviours are clearly defined and documented.
>
> Modify shrink_slab() to use the new API and implement the callouts
> for all the existing shrinkers.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> include/linux/shrinker.h | 37 +++++++++++++++++++++++++----------
> mm/vmscan.c | 51 +++++++++++++++++++++++++++++++-----------------
> 2 files changed, 60 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index ac6b8ee..4f59615 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -4,31 +4,47 @@
> /*
> * This struct is used to pass information from page reclaim to the shrinkers.
> * We consolidate the values for easier extention later.
> + *
> + * The 'gfpmask' refers to the allocation we are currently trying to
> + * fulfil.
> + *
> + * Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
> + * querying the cache size, so a fastpath for that case is appropriate.
> */
> struct shrink_control {
> gfp_t gfp_mask;
>
> /* How many slab objects shrinker() should scan and try to reclaim */
> - unsigned long nr_to_scan;
> + long nr_to_scan;
Why convert from unsigned? What's a poor shrinker to do with a negative
to-scan request?
[snip]
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