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Date:   Tue, 26 Oct 2021 19:08:01 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: move more expensive part of XA setup out of mapping
 check
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On Tue, Oct 26, 2021 at 10:01:20AM -0600, Jens Axboe wrote:
> The fast path here is not needing any writeback, yet we spend time setting
> up the xarray lookup data upfront. Move the part that actually needs to
> iterate the address space mapping into a separate helper, saving ~30% of
> the time here.

No objection to this patch, but it did remind me that I never saw an answer to
https://lore.kernel.org/all/CAHk-=wg_-EwefQ_3Osz4iJxTrTk3tfrV53Z7-jaGg=tm9i5TXg@mail.gmail.com/
(and nor did lore)