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N/C2c21F5yccNRNyt2G5FpnDPIe20/EIBZkrcXANRuD3sRWEV9RKrXCeHXUXd1g6BqvQ1ZI7D7LIL4nx94kBUsUy5eQFSryYubYmXWmqZbXHAgZkFx6aJdBR0olpLyiuOBnTisa0y027FBSCGZ144Qd/7OKnoyzKEUpkqg2QOwYKUb0JH8YvehFzPtluKFiXJ98gzvYLFXnh+IrQgtxSqA9Wmy5dnOjYQGb7XcJNqkn4j5uBqg+i0rze6IADd3lyrS4ZEwYP7kGGkok0HUvHF042KLNlPTDZaNIbeHk6kg5jmwcqUgYL5WYs+Ike9523QXwaTTDeieBO66WvtRfNALzIZqV4U4vT41IoUGJg/tvp74qhTP5M24VJdSNIdlYZhc1RQgAj5fG0miO9dUATpF1YjQ+owoonE7phNmElsbenS2QXjf8eE17lpqQWaeF6mZBBP3fOTfavEWR0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/07/2026 13:52, Lorenzo Stoakes (ARM) wrote: > On Fri, Jul 17, 2026 at 10:58:45AM -0400, Zi Yan wrote: >> On 17 Jul 2026, at 9:36, Lorenzo Stoakes (ARM) wrote: >>> Maybe a simpler version would be to just attack the issue we actually have >>> with it - it uses too much damn memory :) >>> >>> So maybe something like the attached? (you'd probably want to make this a >>> sysctl or at least a defined value of course) >> >> The approach below makes sense to me. In terms of the actual cap size, >> I asked Codex to check what possible pageblock_size and their reserved >> sizes: >> >> 1. 1MB pageblock size (s390) and 11MB per zone, >> 2. 2MB pageblock size and 22MB per zone, >> 3. 8MB pageblock size and 88MB per zone, >> 4. 16MB pageblock size and 176MB per zone, >> 5. 32MB pageblock size and 352MB per zone, >> 6. 128MB pageblock size and 1.375GB per zone, >> 7. 512MB pageblock size and 5.5GB per zone. >> >> 1GB makes sense to me. 512MB might also work. > > Yeah I felt this was a bit of a 'dumb' solution but ultimately if we are > saying 'restrict how much memory this uses to something sane' then that's > what we should just do. > > It might be a good bandaid at least for this issue which is ongoing, well > known, and painful. > > I think at 352MB per zone and 2-3 zones for 32 MiB pageblock, plus reserves > of 2*512 MiB for 512 MiB pageblock makes 1 GiB a sensible choice here > overall. It's worth noting that while users who need more headroom can simply raise min_free_kbytes further via sysctl, those who wish to lower the value can't set it persistently since set_recommended_min_free_kbytes() may raise it back to the recommended value. I think 1 GiB sounds good, but given this behavior where raising is more accessible than lowering, I wonder if we should opt for a lower value. A new sysctl for the cap could address this, but I'm not sure whether adding one would be justified.