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Tue, 23 Jun 2026 00:12:49 -0700 (PDT) From: Ritesh Harjani (IBM) To: Barry Song Cc: linux-mm@kvack.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , David Hildenbrand , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Sayali Patil Subject: Re: [PATCH v4 3/3] powerpc: Kconfig: Enable THP_SWAP on Book3S64 In-Reply-To: Date: Tue, 23 Jun 2026 12:36:22 +0530 Message-ID: <1pdxybv5.ritesh.list@gmail.com> References: X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Barry Song writes: > On Fri, Jun 19, 2026 at 12:41 PM Ritesh Harjani (IBM) > wrote: >> >> THP_SWAP avoids splitting of a transparent huge folio into 32 smaller >> 64K folios (Radix-64K pagesize / 2M PMD) or into 256 smaller 64K folios >> (Hash-64K pagesize / 16M PMD), during swapout. This improves the >> swapping performance since all the bookking & I/O submission happens >> once per large folio. More details at [1]. >> >> PowerPC Book3S64 could not enable this before because PMD_ORDER is >> selected at runtime depending upon the chosen MMU. The earlier patches >> in this series turn SWAPFILE_CLUSTER into a runtime value and introduce >> an ARCH_MAX_PMD_ORDER upperbound override for SWAP_NR_ORDERS. With those >> changes, we can now enable THP SWAP for Book3S64. >> >> This increases bandwidth throughput with zram backend for swapout by >> 40-50% with Radix and 100-130% with Hash (Tested by Sayali) > > Thanks! > > I am curious about the contents of the anonymous memory being tested > and the compression algorithm used by zram. > I am sure it was derived from your microbenchmark itself which you had shared here (so repetitive pattern) with default zram compression algorithm. Thanks for that :) https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d0637c505f I think I got your point - I can mention that it was a microbenchmark similar to yours and not a real world workload test. Is this what you meant here? -ritesh >> >> [1]: https://lore.kernel.org/all/20170515112522.32457-2-ying.huang@intel.com/ > > Best Regards > Barry