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References: <20240611024516.1375191-1-yosryahmed@google.com> <20240611024516.1375191-2-yosryahmed@google.com>
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From: Nhat Pham <nphamcs@gmail.com>
Date: Tue, 11 Jun 2024 09:32:56 -0700
Message-ID: <CAKEwX=OatEx57bOFBb5KNwvDhp4gMZhpjKw356fj4xzanqMJHw@mail.gmail.com>
Subject: Re: [PATCH v3 2/3] mm: zswap: add zswap_never_enabled()
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, 
	Chengming Zhou <chengming.zhou@linux.dev>, Barry Song <21cnbao@gmail.com>, 
	Chris Li <chrisl@kernel.org>, David Hildenbrand <david@redhat.com>, 
	Matthew Wilcox <willy@infradead.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Mon, Jun 10, 2024 at 7:45=E2=80=AFPM Yosry Ahmed <yosryahmed@google.com>=
 wrote:
>
> Add zswap_never_enabled() to skip the xarray lookup in zswap_load() if
> zswap was never enabled on the system. It is implemented using static
> branches for efficiency, as enabling zswap should be a rare event. This
> could shave some cycles off zswap_load() when CONFIG_ZSWAP is used but
> zswap is never enabled.
>
> However, the real motivation behind this patch is two-fold:
> - Incoming large folio swapin work will need to fallback to order-0
>   folios if zswap was ever enabled, because any part of the folio could
>   be in zswap, until proper handling of large folios with zswap is
>   added.
>
> - A warning and recovery attempt will be added in a following change in
>   case the above was not done incorrectly. Zswap will fail the read if
>   the folio is large and it was ever enabled.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>

This LGTM.
Reviewed-by: Nhat Pham <nphamcs@gmail.com>