linux-kernel - TLB flush question (x86

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Date:	Sat, 3 Sep 2011 00:47:48 -0500
From:	Arkaprava Basu <arkaprava.basu@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: TLB flush question (x86_64)

Hello,

     I am using 2.6.31 kernel on x86_64 (with SMP configuration). I
have a confusion on a TLB flush function.
     I found that the method tlb_flush_mmu (include/asm-generic/tlb.h)
, which is called by many system calls like munmap,madvise,mprotect
etc; ignores the virtual address range (start and end parameters) for
which it is called. It internally calls tlb_flush method, which on x86
gets converted to flush_tlb_mm. It seems that flush_tlb_mm flushes out
all the mappings for a given mm_struct (i.e., the whole user address
space for a process) from the tlb. Is there any particular reason why
the entire address space is flushed from the tlb while only a range of
virtual address space was supposedly required to be flushed? For
example why the method flush_tlb_range , which would have flushed
mappings belonging to a given virtual address range only could not
have been used instead of flush_tlb_mm? Is there any performance or
some other correctness related concern for not doing that?

Thanks
Arka
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