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To: Yosry Ahmed Cc: "Sridhar, Kanchana P" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "hannes@cmpxchg.org" , "chengming.zhou@linux.dev" , "usamaarif642@gmail.com" , "ryan.roberts@arm.com" , "21cnbao@gmail.com" <21cnbao@gmail.com>, "ying.huang@linux.alibaba.com" , "akpm@linux-foundation.org" , "senozhatsky@chromium.org" , "sj@kernel.org" , "kasong@tencent.com" , "linux-crypto@vger.kernel.org" , "herbert@gondor.apana.org.au" , "davem@davemloft.net" , "clabbe@baylibre.com" , "ardb@kernel.org" , "ebiggers@google.com" , "surenb@google.com" , "Accardi, Kristen C" , "Gomes, Vinicius" , "Feghali, Wajdi K" , "Gopal, Vinodh" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam01 X-Stat-Signature: bgjx6wffftq3khuy1iydw55fpb7c8cwj X-Rspam-User: X-Rspamd-Queue-Id: 10075A0002 X-HE-Tag: 1760567779-892175 X-HE-Meta: U2FsdGVkX1+cHVXJhk3s+eErQhpVSFAaOmYNwgSa5MOPg2dkxaTqyUV6/Qx3HOSirf3zI/AKqV7/uMaM/Jacm0KL/iacLcAIoEA/EQBZ5pwWtBYJvwg/ecQ0PzbXEbrBa3A/ulk+l5VBCevFFpCVlULSkP0GVvAtmJMC3WxDtqSkHZzwUQ2QjjXSY4E+Y2FoZBAixLRUcH7fHDCVtNril62fYzi2N2PiBjcbhzO1IeN3aoLaJk1L/Q18Y70u2Ew6M0n2rme+iUHQuPh44REstI4nR1qQY6VJcSAGQQ4jtAUEdsaHVEqJ+LRJlS9zJ8y8nQKr1Q6IFPeKZpUQkdYM9yUlNAdun5++lex6vbOOsuHShn5Rp6RKNaj34FAWd8DjeelBcyFQi2CXa1ggDSyjaOhNTPsLlX8rU4KR/jB5ukQhC2KAvbfXiX96tVh8/ZVkdG3yfD3awXxAuP1s95Hx9p9ipCNYu8yYUUbWgjSUNUP9W226uTUgXF0ZY6/kVMI+uZ6YGZHr9b/EJigJ8nj1IUnwYv6GGN+azcRIbLfzmOfs3MZzbaor5KtFTIgZUxRjI148zWqOT2o5HeaFPRQrnySYLzAhTf6CIREI25aak5vSqgZYXrU15Mc72Z9YlFkZRQHa0rVBgoRH/5jDAsXiwNTsYPc1cOlV4qGrpvGajaEyhG6Xg28ZuO2Che1+SrBKdgIs1fqRPw3h/gkfeBMWVHk27TZX5QRigDQZ07KUdGwJeRyc9tWksAo1TaiJFby0M5Xn1THaUQq2BSEAz5tZTiMYyTjHrCSe9ZjDAtHEB4wM6XsAwbuOX+v6EvoU9+043KubrnPDRDZflmwqH+geZMISTXlLb43OG1kBJ/V+g/Q3sRrC48uNTmHzzxJgLE+MvGXiI+BpjGmS/aa3AoXzW0JrDmnxHCKgMw00mND2DUBE+e/1P8y5Hc15TGP+XIHtONFYk56K+YoghQQu00K TTPD26FE bWgvkSHCXMInbPDe+yCwRNl2g89eSPlbp8JYU2RaAyeW8o999ihhc0qZ9DQETiCKaGoTswymOrqI3phQQ8tc/jD7SlL+W9rqS57ltca78Avr6ilnOaK7/NYUate80FZFAzjbzQBO6gZIIT4fbbAlfO6IAjhP7Mzh/yQ/RaICVG8mHynj+FXZ65c6b0BOcw+yKM/G0RXaUo2qPOq8+Se2mbo8FENkU9n3vkjIviKW7HR0aOl1tvk9xIzwFXg891Frr9Vaq3dP9O3cLYT9xRhDoucOejyUkE63HMOZM5R6cRck8YDwLoFg/ME8fGI478xHiKH9KElR/gJdRB9lPIKDaScpXdHjMjksdug4h5/fr2oLudpjagdlyQPFP3v0LiAnWAReCr0DwI8PhNdTk+t1GUMuSG2PrSVicWhEhHXo/OpgDDBoutYY+7givi8UDKkOnzwbM X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 15, 2025 at 3:24=E2=80=AFPM Yosry Ahmed = wrote: > > On Wed, Oct 15, 2025 at 10:15:12PM +0000, Sridhar, Kanchana P wrote: > > I am against increasing the size of struct zswap_entry. On x86_64, there > is a 3 byte hole after 'referenced'. We can technically use that, > although the node id is usually an int, which is 4 bytes on x86_64. > > In practice, I think 2 bytes (i.e. short) should be enough, but it will > be ugly to cast the node id to a short. We should at least WARN on > overflow. Can we pack length and referenced using bit fields? I assume compressed length cannot exceed 2^31 - 1? :) So, something along the line of: struct { unsigned int length:31; bool referenced:1; } That way, we save up another 4 bytes hole, which can be repurposed for the node's id. Does that work? I'm not very experienced with this magickery - please fact check me :) > > Or we can take the simple route and drop the bulk allocation. Or this :)