On Thu, Nov 12, 2020 at 05:12:39PM -0800, Andrew Morton wrote: > On Thu, 12 Nov 2020 16:19:26 -0800 Roman Gushchin <guro@xxxxxx> wrote: > > > >From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001 > > From: Roman Gushchin <guro@xxxxxx> > > Date: Wed, 16 Sep 2020 15:43:48 -0700 > > Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab > > caches with SLAB_ACCOUNT > > > > In general it's unknown in advance if a slab page will contain > > accounted objects or not. In order to avoid memory waste, an > > obj_cgroup vector is allocated dynamically when a need to account > > of a new object arises. Such approach is memory efficient, but > > requires an expensive cmpxchg() to set up the memcg/objcgs pointer, > > because an allocation can race with a different allocation on another > > cpu. > > > > But in some common cases it's known for sure that a slab page will > > contain accounted objects: if the page belongs to a slab cache with a > > SLAB_ACCOUNT flag set. It includes such popular objects like > > vm_area_struct, anon_vma, task_struct, etc. > > > > In such cases we can pre-allocate the objcgs vector and simple assign > > it to the page without any atomic operations, because at this early > > stage the page is not visible to anyone else. > > > > v2: inline set_page_objcgs() and add some comments, by Johannes > > Had me confused! I was looking for the inlined function > set_page_objcgs(). I think "open-code" is a better term here than > "inline". Sorry for the confusion! And thanks for picking up the new version! Roman
