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b=ABYXK6phgiAsHFNuoPmcwPAKZKbjqsrEAOy9MD6FhYm7uRrfD1i/DNLKnTgf7oJgW Fi2MTKejoxt7bkYLd9np7oVFzl1JQZRCCBv/jowNOBu7jRsSJ0mwOZS3bmfA7OiZ4T A+LZ/S8iw4lu5eLfJ/ynIATUp/U/Gc9BnXTC2H30oT5AZBSxBPy0K0nZZmzIFdT091 TqWX+yxWYslkHeodxw4oZfp9xpul3nVweoO4yBitLCOAqWbtRhe3dvVMKudyVpo483 YbPLUa3Ved3bGxlDU07RsRZ/sLrIMieJxe2A+Com/HU4I2jGLe9Q2A1aoZNEjdkttT IPNj0oww2Txkg== Date: Sat, 28 Sep 2024 13:20:45 +0000 To: Danilo Krummrich From: Benno Lossin Cc: ojeda@kernel.org, alex.gaynor@gmail.com, wedsonaf@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, a.hindborg@samsung.com, aliceryhl@google.com, akpm@linux-foundation.org, daniel.almeida@collabora.com, faith.ekstrand@collabora.com, boris.brezillon@collabora.com, lina@asahilina.net, mcanal@igalia.com, zhiw@nvidia.com, cjia@nvidia.com, jhubbard@nvidia.com, airlied@redhat.com, ajanulgu@redhat.com, lyude@redhat.com, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v7 13/26] rust: alloc: implement kernel `Vec` type Message-ID: <0d71296c-e605-47cb-a8be-8cd16c54d9d4@proton.me> In-Reply-To: References: <20240911225449.152928-1-dakr@kernel.org> <20240911225449.152928-14-dakr@kernel.org> <1a06b767-ca02-41ec-840a-47e73f7876d8@proton.me> Feedback-ID: 71780778:user:proton X-Pm-Message-ID: 341fb30362b194ab6bb6b8b04e97d79a43f2503d MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 8f3qauqp57ecjt6xwnmf3u6xhc641m58 X-Rspamd-Queue-Id: CDFE8180002 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1727529654-856865 X-HE-Meta: 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 yg5pBJoU BVqEcWhgW6v/dfYKRL32aCg23hu2LId1WUajyIs/F1aVs2miXbvlWDdyj/Zqb0UQ8skFOkKSrtDfnA/t/J/pdX2rh4d7I62yxU6HCcXTGFWnOHjnmO1r9JRFqX/G8BiZNwM13O/g7Zl+/HRjc3wAxFVG2+OH5frPw05UGCl8Z2kSsZoC618QMyKR0G7dLdRk5ztg/SjsoHYOrWl+jPiKhjNxx2Nh4FV6ZE/D+OyW9gJROqJA8AotKXPWPVZluD7/IFZ3AEwm8uYnBIyF7MbEVp834ICskszIvDE80gxnWykxol4mwf1Ul913YfK51cZ/bcPZE0JsYjHzhy5p5DqcC+SSky4ajsOUp4UFDZrUONVTaQJX3d+Vs07Xgxw0CQ7udb9eiefxBcu2ClCMg4QH0Kvlss/8WsJ26oKNhsLpfplWZLg1kBVz9uWh1g9/e3mv5mv8xsdsbrC2NN6dNDCHTzeqOj7Z68gd2sDL7 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 28.09.24 14:43, Danilo Krummrich wrote: > On Thu, Sep 26, 2024 at 01:47:04PM +0000, Benno Lossin wrote: >> On 12.09.24 00:52, Danilo Krummrich wrote: >>> + /// Appends an element to the back of the [`Vec`] instance. >>> + /// >>> + /// # Examples >>> + /// >>> + /// ``` >>> + /// let mut v =3D KVec::new(); >>> + /// v.push(1, GFP_KERNEL)?; >>> + /// assert_eq!(&v, &[1]); >>> + /// >>> + /// v.push(2, GFP_KERNEL)?; >>> + /// assert_eq!(&v, &[1, 2]); >>> + /// # Ok::<(), Error>(()) >>> + /// ``` >>> + pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocErro= r> { >>> + Vec::reserve(self, 1, flags)?; >>> + >>> + // SAFETY: >>> + // - `self.len` is smaller than `self.capacity` and hence, the= resulting pointer is >>> + // guaranteed to be part of the same allocated object. >>> + // - `self.len` can not overflow `isize`. >>> + let ptr =3D unsafe { self.as_mut_ptr().add(self.len) }; >>> + >>> + // SAFETY: >>> + // - `ptr` is properly aligned and valid for writes. >>> + unsafe { core::ptr::write(ptr, v) }; >> >> Why not use `self.spare_capacity_mut()[0].write(v);`? >=20 > Before v7 I did exactly that, but in v6 you suggested to use the raw poin= ter > instead to avoid the bounds check. Ah I see... Would be pretty useful for me to have my previous comments easily accessible, I don't usually look at the previous thread. Is anyone aware of some tools for that? >> If you want to avoid the bounds check, you can do >> >> let first =3D self.spare_capacity_mut().first(); >> // SAFETY: the call to `Vec::reserve` above ensures that `spare_capa= city_mut()` is non-empty. >> unsafe { first.unwrap_unchecked() }.write(v); >=20 > `first` does a similar check to create the `Option<&T>`, right?. I'd rath= er keep > the raw pointer access as suggested in v6. It does a check, but the optimizer will get rid of it if you use `unwrap_unchecked` [1]. But feel free to leave it as-is. [1]: https://godbolt.org/z/zYbMTo86M --- Cheers, Benno