linux-kernel - Re: [PATCH v2 2/4] mm: vmalloc: use rwsem, mutex for vmap_area_lock and vmap

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Date:   Fri, 24 Mar 2023 05:31:55 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v2 2/4] mm: vmalloc: use rwsem, mutex for vmap_area_lock
 and vmap_block->lock

On Fri, Mar 24, 2023 at 04:25:39PM +1100, Dave Chinner wrote:
> Did you read the comment above this function? I mean, it's all about
> how poorly kvmalloc() works for the highly concurrent, fail-fast
> context that occurs in the journal commit fast path, and how we open
> code it with kmalloc and vmalloc to work "ok" in this path.
> 
> Then if you go look at the commits related to it, you might find
> that XFS developers tend to write properly useful changelogs to
> document things like "it's better, but vmalloc will soon have lock
> contention problems if we hit it any harder"....

The problem with writing whinges like this is that mm developers don't
read XFS changelogs.  I certainly had no idea this was a problem, and
I doubt anybody else who could make a start at fixing this problem had
any idea either.  Why go to all this effort instead of sending an email
to linux-mm?