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Date: Wed, 20 Mar 2024 19:46:38 +0000
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Subject: Re: [PATCH v7] zswap: replace RB tree with xarray
From: Yosry Ahmed <yosryahmed@google.com>
To: Chris Li <chrisl@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Andrew Morton <akpm@linux-foundation.org>, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, 
	Nhat Pham <nphamcs@gmail.com>, "Matthew Wilcox (Oracle)" <willy@infradead.org>, 
	Chengming Zhou <zhouchengming@bytedance.com>, Barry Song <v-songbaohua@oppo.com>
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On Wed, Mar 20, 2024 at 12:41:48PM -0700, Chris Li wrote:
> On Wed, Mar 20, 2024 at 12:34=E2=80=AFPM Yosry Ahmed <yosryahmed@google.c=
om> wrote:
> > > you can expect it to be coherent.
> >
> > Fair enough, but don't we still need a barrier there? Couldn't some
> > initializations still be reorder after zswap_lru_add()?
>=20
> I am under the impression that the lru list handling function already
> handles the barrier. If an explicit barrier is needed, wouldn't all
> other lru callers have barriers sprinkling all over the place?

list_lru_add() holds a lock, which implies a compiler barrier. I was
wondering if we need smp_wmb() to prevent other CPUs from observing a
partially initialized entry during writeback.

I am not sure if the list lru makes such assumptions about the need for
barriers.