lkml.org 
[lkml]   [2020]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag
On Wed, Sep 30, 2020 at 05:27:10PM -0700, Roman Gushchin wrote:
> PageKmemcg flag is currently defined as a page type (like buddy,
> offline, table and guard). Semantically it means that the page
> was accounted as a kernel memory by the page allocator and has
> to be uncharged on the release.
>
> As a side effect of defining the flag as a page type, the accounted
> page can't be mapped to userspace (look at page_has_type() and
> comments above). In particular, this blocks the accounting of
> vmalloc-backed memory used by some bpf maps, because these maps
> do map the memory to userspace.
>
> One option is to fix it by complicating the access to page->mapcount,
> which provides some free bits for page->page_type.
>
> But it's way better to move this flag into page->memcg_data flags.
> Indeed, the flag makes no sense without enabled memory cgroups
> and memory cgroup pointer set in particular.
>
> This commit replaces PageKmemcg() and __SetPageKmemcg() with
> PageMemcgKmem() and an open-coded OR operation setting the memcg
> pointer with the MEMCG_DATA_KMEM bit. __ClearPageKmemcg() can be
> simple deleted, as the whole memcg_data is zeroed at once.
>
> As a bonus, on !CONFIG_MEMCG build the PageMemcgKmem() check will
> be compiled out.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

\
 
 \ /
  Last update: 2020-10-01 15:51    [W:0.127 / U:0.912 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site