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

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Date:   Wed, 15 May 2019 17:18:05 +0000
From:   Roman Gushchin <guro@...com>
To:     Anshuman Khandual <anshuman.khandual@....com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <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 Wed, May 15, 2019 at 09:57:11AM +0530, Anshuman Khandual wrote:
> 
> 
> 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%.

So you can confirm my numbers? Great, thank you!