linux-kernel - Re: [PATCH v4 09/66] mm/mmap: Use the maple tree in find

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Date:   Thu, 13 Jan 2022 16:46:52 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 09/66] mm/mmap: Use the maple tree in find_vma()
 instead of the rbtree.

On 12/15/21 19:09, Liam Howlett wrote:
>> - the future lookup of address vma->vm_end will return this vma, although
>> the address doesn't belong to it. Wouldn't be surprised if this caused
>> infrequent mysterious bugs?
>>
>> Both will resolve with vmacache removal later, but better still fix this.
> This is certainly worth fixing.  I am surprised that I did not hit a
> random bug as you said above, I would expect it to occur as well.
> Although, I didn't run each patch individually for long unless I was
> tracking down an issue on a rebase.

Ah, it doesn't cause a bug because vmacache_find() checks the boundaries of
vmas in the vmacache.