linux-kernel - Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page

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Date:   Fri, 13 Apr 2018 15:29:41 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Chintan Pandya <cpandya@...eaurora.org>, vbabka@...e.cz,
        labbott@...hat.com, catalin.marinas@....com, hannes@...xchg.org,
        f.fainelli@...il.com, xieyisheng1@...wei.com,
        ard.biesheuvel@...aro.org, richard.weiyang@...il.com,
        byungchul.park@....com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range

On 04/13/2018 02:46 PM, Chintan Pandya wrote:
> Unmap legs do call vunmap_page_range() irrespective of
> debug_pagealloc_enabled() is enabled or not. So, remove
> redundant check and optional vunmap_page_range() routines.

vunmap_page_range() tears down the page table entries and does
not really flush related TLB entries normally unless page alloc
debug is enabled where it wants to make sure no stale mapping is
still around for debug purpose. Deferring TLB flush improves
performance. This patch will force TLB flush during each page
table tear down and hence not desirable.