linux-kernel - [RFC 0/3] Group pages on the direct map for permissioned vmallocs

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Date:   Mon,  5 Apr 2021 13:37:08 -0700
From:   Rick Edgecombe <rick.p.edgecombe@...el.com>
To:     akpm@...ux-foundation.org, linux-mm@...ck.org, bpf@...r.kernel.org,
        dave.hansen@...ux.intel.com, peterz@...radead.org, luto@...nel.org,
        jeyu@...nel.org
Cc:     linux-kernel@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, hch@...radead.org, x86@...nel.org,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: [RFC 0/3] Group pages on the direct map for permissioned vmallocs

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