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amd64 pmap: patch up a comment in pmap_init_pv_table

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Requested by:	jhb
This commit is contained in:
Mateusz Guzik 2023-02-06 22:33:28 +00:00
parent 393b0ba25f
commit 819ed47204
1 changed files with 7 additions and 3 deletions
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10
sys/amd64/amd64/pmap.c
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@ -2314,9 +2314,13 @@ pmap_init_pv_table(void)
int domain, i, j, pages;
/*
* We strongly depend on the size being a power of two, so the assert
* is overzealous. However, should the struct be resized to a
* different power of two, the code below needs to be revisited.
* For correctness we depend on the size being evenly divisible into a
* page. As a tradeoff between performance and total memory use, the
* entry is 64 bytes (aka one cacheline) in size. Not being smaller
* avoids false-sharing, but not being 128 bytes potentially allows for
* avoidable traffic due to adjacent cacheline prefetcher.
*
* Assert the size so that accidental changes fail to compile.
*/
CTASSERT((sizeof(*pvd) == 64));