On Mon, Apr 16, 2018 at 1:51 PM, Shakeel Butt [off-list ref] wrote:

Introduce the memcg variant for kmalloc[_node] and
kmem_cache_alloc[_node].  For kmem_cache_alloc, the kernel switches the
root kmem cache with the memcg specific kmem cache for __GFP_ACCOUNT
allocations to charge those allocations to the memcg.  However, the memcg
to charge is extracted from the current task_struct.  This patch
introduces the variant of kmem cache allocation functions where the memcg
can be provided explicitly by the caller instead of deducing the memcg
from the current task.

The kmalloc allocations are underlying served using the kmem caches unless
the size of the allocation request is larger than KMALLOC_MAX_CACHE_SIZE,
in which case, the kmem caches are bypassed and the request is routed
directly to page allocator.  So, for __GFP_ACCOUNT kmalloc allocations,
the memcg of current task is charged.  This patch introduces memcg variant
of kmalloc functions to allow callers to provide memcg for charging.

These functions are useful for use-cases where the allocations should be
charged to the memcg different from the memcg of the caller.  One such
concrete use-case is the allocations for fsnotify event objects where the
objects should be charged to the listener instead of the producer.

One requirement to call these functions is that the caller must have the
reference to the memcg.  Using kmalloc_memcg and kmem_cache_alloc_memcg
implicitly assumes that the caller is requesting a __GFP_ACCOUNT
allocation.

Signed-off-by: Shakeel Butt <redacted>

I will send the v6 of this patchset after this merge window. In v6, I
will make memalloc_memcg_[save|restore] scope API similar to NOFS,
NOIO and NORECLAIM APIs.

---
Changelog since v4:
- Removed branch from hot path of memory charging.

Changelog since v3:
- Added node variant of directed kmem allocation functions.

Changelog since v2:
- Merge the kmalloc_memcg patch into this patch.
- Instead of plumbing memcg throughout, use field in task_struct to pass
  the target_memcg.

Changelog since v1:
- Fixed build for SLOB