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Thu, 27 Mar 2025 17:28:41 +0000 Received: from dev-dsk-ptyadav-1c-43206220.eu-west-1.amazon.com (dev-dsk-ptyadav-1c-43206220.eu-west-1.amazon.com [172.19.91.144]) by email-imr-corp-prod-pdx-all-2c-c4413280.us-west-2.amazon.com (Postfix) with ESMTP id 3538AA04D5; Thu, 27 Mar 2025 17:28:41 +0000 (UTC) Received: by dev-dsk-ptyadav-1c-43206220.eu-west-1.amazon.com (Postfix, from userid 23027615) id BF36651B7; Thu, 27 Mar 2025 17:28:40 +0000 (UTC) From: Pratyush Yadav To: Jason Gunthorpe CC: Changyuan Lyu , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation In-Reply-To: References: <20250320015551.2157511-1-changyuanl@google.com> <20250320015551.2157511-10-changyuanl@google.com> Date: Thu, 27 Mar 2025 17:28:40 +0000 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250327_102845_496841_DFF9D4D0 X-CRM114-Status: GOOD ( 20.37 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Mar 27 2025, Jason Gunthorpe wrote: > On Thu, Mar 27, 2025 at 10:03:17AM +0000, Pratyush Yadav wrote: > >> Of course, with the current linked list structure, this cannot work. But >> I don't see why we need to have it. I think having a page-table like >> structure would be better -- only instead of having PTEs at the lowest >> levels, you have the bitmap. > > Yes, but there is a trade off here of what I could write in 30 mins > and what is maximally possible :) The xarray is providing a page table > implementation in a library form. > > I think this whole thing can be optimized, especially the > memblock_reserve side, but the idea here is to get started and once we > have some data on what the actual preservation workload is then > someone can optimize this. > > Otherwise we are going to be spending months just polishing this one > patch without any actual data on where the performance issues and hot > spots actually are. The memblock_reserve side we can optimize later, I agree. But the memory preservation format is ABI and I think that is worth spending a little more time on. And I don't think it should be that much more complex than the current format. I want to hack around with it, so I'll give it a try over the next few days and see what I can come up with. -- Regards, Pratyush Yadav