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Subject[RFC 0/3] Group pages on the direct map for permissioned vmallocs
Date
Hi,

This is a followup to the previous attempt to overhaul how vmalloc permissions
are done:
https://lore.kernel.org/lkml/20201120202426.18009-1-rick.p.edgecombe@intel.com/

In working on a next version it dawned on me that we can significantly reduce
direct map breakage on x86 with a much less invasive change, so I thought maybe
I would start there in the meantime.

In a test of booting fedora and running the BPF unit tests, this reduced 4k
direct map pages by 98%.

It simply uses pages for x86 module_alloc() mappings from a cache created out of
2MB pages. This results in all the later breakage clustering in 2MB blocks on
the direct map. The trade-off is colder pages are used for these allocations.
All module_alloc() users (modules, ebpf jit, ftrace, kprobes) get this behavior.

Potentially this behavior should be enabled for eBPF byte code allocations as
well in the case of !CONFIG_BPF_JIT_ALWAYS_ON.

The new APIs and invasive changes in the callers can happen after vmalloc huge
pages bring more benefits. Although, I can post shootdown reduction changes with
previous comments integrated if anyone disagrees.

Based on v5.11.

Thanks,

Rick


Rick Edgecombe (3):
list: Support getting most recent element in list_lru
vmalloc: Support grouped page allocations
x86/module: Use VM_GROUP_PAGES flag

arch/x86/Kconfig | 1 +
arch/x86/kernel/module.c | 2 +-
include/linux/list_lru.h | 13 +++
include/linux/vmalloc.h | 1 +
mm/Kconfig | 9 ++
mm/list_lru.c | 28 +++++
mm/vmalloc.c | 215 +++++++++++++++++++++++++++++++++++++--
7 files changed, 257 insertions(+), 12 deletions(-)

--
2.29.2

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