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Subject: Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range
To:     Anshuman Khandual <khandual@linux.vnet.ibm.com>, vbabka@suse.cz,
        labbott@redhat.com, catalin.marinas@arm.com, hannes@cmpxchg.org,
        f.fainelli@gmail.com, xieyisheng1@huawei.com,
        ard.biesheuvel@linaro.org, richard.weiyang@gmail.com,
        byungchul.park@lge.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <1523611019-17679-1-git-send-email-cpandya@codeaurora.org>
 <a623e12b-bb5e-58fa-c026-de9ea53c5bd9@linux.vnet.ibm.com>
From:   Chintan Pandya <cpandya@codeaurora.org>
Message-ID: <8da9f826-2a3d-e618-e512-4fc8d45c16f2@codeaurora.org>
Date:   Fri, 13 Apr 2018 15:47:02 +0530
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On 4/13/2018 3:29 PM, Anshuman Khandual wrote:
> 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.
> 
Deferred TLB invalidation will surely improve performance. But force
flush can help in detecting invalid access right then and there. I
chose later. May be I should have clean up the vmap tear down code
as well where it actually does the TLB invalidation.

Or make TLB invalidation in free_unmap_vmap_area() be dependent upon
debug_pagealloc_enabled().

Chintan
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