Hello Michal,
Thanks for your comment :)
On Tue, 24 Feb 2015, Michal Hocko wrote:
On Tue 24-02-15 04:54:18, SeongJae Park wrote:
[...]
include/linux/cma.h | 4 +
include/linux/gcma.h | 64 +++
mm/Kconfig | 24 +
mm/Makefile | 1 +
mm/cma.c | 113 ++++-
mm/gcma.c | 1321 ++++++++++++++++++++++++++++++++++++++++++++++++++
6 files changed, 1508 insertions(+), 19 deletions(-)
create mode 100644 include/linux/gcma.h
create mode 100644 mm/gcma.c
Wow this is huge! And I do not see reason for it to be so big. Why
cannot you simply define (per-cma area) 2-class users policy? Either via
kernel command line or export areas to userspace and allow to set policy
there.
For implementation of the idea, we should develop not only policy
selection, but also backend for discardable memory. Most part of this
patch were made for the backend.
Current implementation gives selection of policy per cma area to users.
Only about 120 lines of code were changed for that though it's most ugly
part of this patch. The part remains as ugly in this RFC because this is
just prototype. The part will be changed in next version patchset.
For starter something like the following policies should suffice AFAIU
your description.
- NONE - exclusive pool for CMA allocations only
- DROPABLE - only allocations which might be dropped without any
additional actions - e.g. cleancache and frontswap with
write-through policy
- RECLAIMABLE - only movable allocations which can be migrated
or dropped after writeback.
Has such an approach been considered?
Similarly, but not in same way. In summary, GCMA gives DROPABLE and
RECLAIMABLE policy selection per cma area and NONE policy to entire cma
area declared using GCMA interface.
In detail, user could set policy of cma area as gcma way(DROPABLE) or cma
way(RECLAIMABLE). Also, user could set gcma to utilize their cma area with
Cleancache and/or Frontswap or not(NONE policy).
Your suggestion looks simple and better to understand. Next version of
gcma will let users to be able to select policy as those per cma area.
Thanks,
SeongJae Park
--
Michal Hocko
SUSE Labs
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