linux-kernel - [PATCH] Documentation/features: mark BATCHED_UNMAP_TLB

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Date:   Tue, 23 Feb 2021 13:32:30 +1300
From:   Barry Song <song.bao.hua@...ilicon.com>
To:     <corbet@....net>, <linux-doc@...r.kernel.org>,
        <akpm@...ux-foundation.org>, <linux-mm@...ck.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...neuler.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Mel Gorman <mgorman@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH] Documentation/features: mark BATCHED_UNMAP_TLB_FLUSH doesn't apply to ARM64

BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
sending one IPI to TLB flush all entries after unmapping pages rather
than sending an IPI to flush each individual entry.
On arm64, tlb shootdown is done by hardware. Flush instructions are
innershareable. The local flushes are limited to the boot (1 per CPU)
and when a task is getting a new ASID.
So marking this feature as "TODO" is not proper. ".." isn't good as
well. So this patch adds a "N/A" for this kind of features which are
not needed on some architectures.

Cc: Mel Gorman <mgorman@...e.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
---
 Documentation/features/arch-support.txt        | 1 +
 Documentation/features/vm/TLB/arch-support.txt | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/features/arch-support.txt b/Documentation/features/arch-support.txt
index d22a1095e661..118ae031840b 100644
--- a/Documentation/features/arch-support.txt
+++ b/Documentation/features/arch-support.txt
@@ -8,4 +8,5 @@ The meaning of entries in the tables is:
     | ok |  # feature supported by the architecture
     |TODO|  # feature not yet supported by the architecture
     | .. |  # feature cannot be supported by the hardware
+    | N/A|  # feature doesn't apply to the architecture
 
diff --git a/Documentation/features/vm/TLB/arch-support.txt b/Documentation/features/vm/TLB/arch-support.txt
index 30f75a79ce01..0d070f9f98d8 100644
--- a/Documentation/features/vm/TLB/arch-support.txt
+++ b/Documentation/features/vm/TLB/arch-support.txt
@@ -9,7 +9,7 @@
     |       alpha: | TODO |
     |         arc: | TODO |
     |         arm: | TODO |
-    |       arm64: | TODO |
+    |       arm64: | N/A  |
     |         c6x: |  ..  |
     |        csky: | TODO |
     |       h8300: |  ..  |
-- 
2.25.1