linux-kernel - Re: [PATCH] mm: refactor __vunmap() to avoid duplicated call to find_vm

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Date:   Wed, 15 May 2019 09:57:11 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: refactor __vunmap() to avoid duplicated call to
 find_vm_area()



On 05/15/2019 05:21 AM, Roman Gushchin wrote:
> __vunmap() calls find_vm_area() twice without an obvious reason:
> first directly to get the area pointer, second indirectly by calling
> vm_remove_mappings()->remove_vm_area(), which is again searching
> for the area.
> 
> To remove this redundancy, let's split remove_vm_area() into
> __remove_vm_area(struct vmap_area *), which performs the actual area
> removal, and remove_vm_area(const void *addr) wrapper, which can
> be used everywhere, where it has been used before. Let's pass
> a pointer to the vm_area instead of vm_struct to vm_remove_mappings(),
> so it can pass it to __remove_vm_area() and avoid the redundant area
> lookup.
> 
> On my test setup, I've got 5-10% speed up on vfree()'ing 1000000
> of 4-pages vmalloc blocks.

Though results from  1000000 single page vmalloc blocks remain inconclusive,
4-page based vmalloc block's result shows improvement in the range of 5-10%.