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Date: Mon, 16 Nov 2020 10:03:09 -0500 From: Johannes Weiner <hannes@...xchg.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Roman Gushchin <guro@...com>, linux-mm@...ck.org, Shakeel Butt <shakeelb@...gle.com>, Michal Hocko <mhocko@...nel.org>, Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org, kernel-team@...com Subject: Re: [PATCH 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab caches with SLAB_ACCOUNT 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@...com> wrote: > > > >From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001 > > From: Roman Gushchin <guro@...com> > > 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". > > Here's the -fix: > > From: Roman Gushchin <guro@...com> > Subject: mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account-v2 > > open-code set_page_objcgs() and add some comments, by Johannes > > Link: https://lkml.kernel.org/r/20201113001926.GA2934489@carbon.dhcp.thefacebook.com > Signed-off-by: Roman Gushchin <guro@...com> > Cc: Christoph Lameter <cl@...ux.com> > Cc: Johannes Weiner <hannes@...xchg.org> > Cc: Michal Hocko <mhocko@...nel.org> > Cc: Shakeel Butt <shakeelb@...gle.com> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> Thanks! For the combined patch: Acked-by: Johannes Weiner <hannes@...xchg.org>
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