linux-kernel - Re: [PATCH 2/3] mm: avoid slub allocation while holding list

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Message-ID: <20190912013100.GA114178@google.com>
Date:   Wed, 11 Sep 2019 19:31:00 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: avoid slub allocation while holding list_lock

On Thu, Sep 12, 2019 at 03:44:01AM +0300, Kirill A. Shutemov wrote:
> On Wed, Sep 11, 2019 at 06:29:28PM -0600, Yu Zhao wrote:
> > If we are already under list_lock, don't call kmalloc(). Otherwise we
> > will run into deadlock because kmalloc() also tries to grab the same
> > lock.
> > 
> > Instead, statically allocate bitmap in struct kmem_cache_node. Given
> > currently page->objects has 15 bits, we bloat the per-node struct by
> > 4K. So we waste some memory but only do so when slub debug is on.
> 
> Why not have single page total protected by a lock?
> 
> Listing object from two pages at the same time doesn't make sense anyway.
> Cuncurent validating is not something sane to do.

Okay, cutting down to static global bitmap.