linux-kernel - Re: [PATCH 2/3] mm: separate memory allocation and actual work in alloc_vmap

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Message-ID: <20190301164834.GA3154@tower.DHCP.thefacebook.com>
Date:   Fri, 1 Mar 2019 16:48:41 +0000
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     Roman Gushchin <guroan@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH 2/3] mm: separate memory allocation and actual work in
 alloc_vmap_area()

On Fri, Mar 01, 2019 at 03:43:19PM +0100, Vlastimil Babka wrote:
> On 2/25/19 9:30 PM, Roman Gushchin wrote:
> > alloc_vmap_area() is allocating memory for the vmap_area, and
> > performing the actual lookup of the vm area and vmap_area
> > initialization.
> > 
> > This prevents us from using a pre-allocated memory for the map_area
> > structure, which can be used in some cases to minimize the number
> > of required memory allocations.
> 
> Hmm, but that doesn't happen here or in the later patch, right? The only
> caller of init_vmap_area() is alloc_vmap_area(). What am I missing?

So initially the patch was a part of a bigger patchset, which
tried to minimize the number of separate allocations during vmalloc(),
e.g. by inlining vm_struct->pages into vm_struct for small areas.

I temporarily dropped the rest of the patchset for some rework,
but decided to leave this patch, because it looks like a nice refactoring
in any case, and also it has been already reviewed and acked by Matthew
and Johannes.

Thank you for looking into it!