From 742f3c8193a3cb3e444887211214ef0721e3ef8d Mon Sep 17 00:00:00 2001
From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Date: Fri, 7 Dec 2018 09:05:53 +0000
Subject: [PATCH] um: Optimize Flush TLB for force/fork case
When UML handles a fork the page tables need to be brought up
to date. That was done using brute force - full tlb flush.
This is actually unnecessary, because the mapped-in mappings are
all correct and the only mappings which need to be updated
after a flush are any unmaps (so that paging works) as well as
any pending protection changes.
This optimization squeezes out up to 3% from a full kernel rebuild
time under memory pressure.
Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
---
arch/um/kernel/tlb.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
index 9ca902df243a3..8347161c2ae0f 100644
--- a/arch/um/kernel/tlb.c
+++ b/arch/um/kernel/tlb.c
@@ -242,10 +242,11 @@ static inline int update_pte_range(pmd_t *pmd, unsigned long addr,
prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) |
(x ? UM_PROT_EXEC : 0));
if (hvc->force || pte_newpage(*pte)) {
- if (pte_present(*pte))
- ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
- PAGE_SIZE, prot, hvc);
- else
+ if (pte_present(*pte)) {
+ if (pte_newpage(*pte))
+ ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
+ PAGE_SIZE, prot, hvc);
+ } else
ret = add_munmap(addr, PAGE_SIZE, hvc);
} else if (pte_newprot(*pte))
ret = add_mprotect(addr, PAGE_SIZE, prot, hvc);
--
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