Hello Kirill,
I don't have any objections to the idea behind this patch set.
Well, at least I don't know how to better tackle the problem you
describe in the cover letter. Please, see below for my comments
regarding implementation details.
On Wed, Mar 21, 2018 at 04:21:17PM +0300, Kirill Tkhai wrote:
> The patch introduces shrinker::id number, which is used to enumerate
> memcg-aware shrinkers. The number start from 0, and the code tries
> to maintain it as small as possible.
>
> This will be used as to represent a memcg-aware shrinkers in memcg
> shrinkers map.
>
> Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
> ---
> include/linux/shrinker.h | 1 +
> mm/vmscan.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 60 insertions(+)
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index a3894918a436..738de8ef5246 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -66,6 +66,7 @@ struct shrinker {
>
> /* These are for internal use */
> struct list_head list;
> + int id;
This definition could definitely use a comment.
BTW shouldn't we ifdef it?
> /* objs pending delete, per node */
> atomic_long_t *nr_deferred;
> };
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8fcd9f8d7390..91b5120b924f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -159,6 +159,56 @@ unsigned long vm_total_pages;
> static LIST_HEAD(shrinker_list);
> static DECLARE_RWSEM(shrinker_rwsem);
>
> +#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
> +static DEFINE_IDA(bitmap_id_ida);
> +static DECLARE_RWSEM(bitmap_rwsem);
Can't we reuse shrinker_rwsem for protecting the ida?
> +static int bitmap_id_start;
> +
> +static int alloc_shrinker_id(struct shrinker *shrinker)
> +{
> + int id, ret;
> +
> + if (!(shrinker->flags & SHRINKER_MEMCG_AWARE))
> + return 0;
> +retry:
> + ida_pre_get(&bitmap_id_ida, GFP_KERNEL);
> + down_write(&bitmap_rwsem);
> + ret = ida_get_new_above(&bitmap_id_ida, bitmap_id_start, &id);
AFAIK ida always allocates the smallest available id so you don't need
to keep track of bitmap_id_start.
> + if (!ret) {
> + shrinker->id = id;
> + bitmap_id_start = shrinker->id + 1;
> + }
> + up_write(&bitmap_rwsem);
> + if (ret == -EAGAIN)
> + goto retry;
> +
> + return ret;
> +}
