linux-kernel - Re: [RFC PATCH 12/13] fs/userfaultfd: kmem-cache for wait-queue objects

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Date:   Mon, 30 Nov 2020 11:51:22 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH 12/13] fs/userfaultfd: kmem-cache for wait-queue
 objects

> On Nov 28, 2020, at 4:45 PM, Nadav Amit <nadav.amit@...il.com> wrote:
> 
> From: Nadav Amit <namit@...are.com>
> 
> Allocating work-queue objects on the stack has usually negative
> performance side-effects. First, it is hard to ensure alignment to
> cache-lines without increasing the stack size. Second, it might cause
> false sharing. Third, it is more likely to encounter TLB misses as
> objects are more likely reside on different pages.
> 
> Allocate userfaultfd wait-queue objects on the heap using kmem-cache for
> better performance.

Err… The wait-queue objects are still on the stack in some cases that I
missed. Will fix.