linux-kernel - Re: [PATCH v4 2/2] mm/vmalloc.c: Modify struct vmap

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Message-ID: <20190715142754.pw55g4b2l6lzoznn@pc636>
Date:   Mon, 15 Jul 2019 16:27:54 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Pengfei Li <lpf.vector@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>, rpenyaev@...e.de,
        peterz@...radead.org, guro@...com, rick.p.edgecombe@...el.com,
        rppt@...ux.ibm.com, aryabinin@...tuozzo.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] mm/vmalloc.c: Modify struct vmap_area to reduce
 its size

On Fri, Jul 12, 2019 at 11:09:00PM +0800, Pengfei Li wrote:
> On Fri, Jul 12, 2019 at 9:49 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Fri, Jul 12, 2019 at 08:02:13PM +0800, Pengfei Li wrote:
> >
> > I don't think you need struct union struct union.  Because llist_node
> > is just a pointer, you can get the same savings with just:
> >
> >         union {
> >                 struct llist_node purge_list;
> >                 struct vm_struct *vm;
> >                 unsigned long subtree_max_size;
> >         };
> >
> 
> Thanks for your comments.
> 
> As you said, I did this in v3.
> https://patchwork.kernel.org/patch/11031507/
> 
> The reason why I use struct union struct in v4 is that I want to
> express "in the tree" and "in the purge list" are two completely
> isolated cases.
> 
I think that is odd. Your v3 was fine to me. All that mess with
struct union struct makes it weird, so having just comments there
is enough, imho.

<snip>
-               __free_vmap_area(va);
+               merge_or_add_vmap_area(va,
+                       &free_vmap_area_root, &free_vmap_area_list);
+
<snip>
Should not be done in this patch. I can re-spin "mm/vmalloc: do not keep unpurged areas in the busy tree"
and add it there. So, as a result we will not modify unlink_va() function.

Thus, this patch will reduce the size only, and will not touch other parts.

--
Vlad Rezki