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Date:   Wed, 11 Sep 2019 19:31:00 -0600
From:   Yu Zhao <yuzhao@google.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] mm: avoid slub allocation while holding list_lock
Message-ID: <20190912013100.GA114178@google.com>
References: <20190911071331.770ecddff6a085330bf2b5f2@linux-foundation.org>
 <20190912002929.78873-1-yuzhao@google.com>
 <20190912002929.78873-2-yuzhao@google.com>
 <20190912004401.jdemtajrspetk3fh@box>
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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.