linux-kernel - Re: [PATCH v2 1/3] mm: vmalloc: Avoid of calling __find_vmap_area() twise in _

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Date:   Thu, 22 Dec 2022 15:43:42 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH v2 1/3] mm: vmalloc: Avoid of calling __find_vmap_area()
 twise in __vunmap()

On Thu, Dec 22, 2022 at 07:38:14PM +0800, Baoquan He wrote:
> On 12/21/22 at 06:44pm, Uladzislau Rezki (Sony) wrote:
> > Currently __vunmap() path calls __find_vmap_area() two times. One on
> > entry to check that area exists, second time inside remove_vm_area()
> > function that also performs a new search of VA.
> > 
> > In order to improvie it from a performance point of view we split
> > remove_vm_area() into two new parts:
> >   - find_unlink_vmap_area() that does a search and unlink from tree;
> >   - __remove_vm_area() that does a removing but without searching.
> > 
> > In this case there is no any functional change for remove_vm_area()
> > whereas vm_remove_mappings(), where a second search happens, switches
> > to the __remove_vm_area() variant where already detached VA is passed
> > as a parameter, so there is no need to find it again.
> 
> I like this patch. This takes off the va->vm clearning too. Finally I
> don't need to worry about the va->flags clearing during unmapping
> when reading out vmap_block areas.
> 
Thanks. This patch was one of the reason to help out with the per-cpu
busy areas tracking/reading of your work :)

--
Uladzsislau Rezki