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([2620:10d:c092:600::1:87eb]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ac1e02f9660sm213150266b.71.2025.03.04.02.03.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Mar 2025 02:03:56 -0800 (PST) Message-ID: <9a5e3d75-afef-4942-881c-444d35472758@gmail.com> Date: Tue, 4 Mar 2025 10:05:07 +0000 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/8] io_uring: add infra for importing vectored reg buffers To: Caleb Sander Mateos Cc: io-uring@vger.kernel.org, Andres Freund References: <841b4d5b039b9db84aa1e1415a6d249ea57646f6.1741014186.git.asml.silence@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 3/3/25 20:49, Caleb Sander Mateos wrote: > On Mon, Mar 3, 2025 at 7:51 AM Pavel Begunkov wrote: ... > > If I understand correctly, io_import_reg_vec() converts the iovecs to > bio_vecs in place. If an iovec expands to more than one bio_vec (i.e. > crosses a folio boundary), wouldn't the bio_vecs overwrite iovecs that > hadn't been processed yet? It's handled, obviously, you missed that the vectors are offset'ed from each other. > >> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c >> index 9b05e614819e..1ec1f5b3e385 100644 >> --- a/io_uring/rsrc.c >> +++ b/io_uring/rsrc.c ... >> + for (; iov_len; offset = 0, bvec_idx++, src_bvec++) { >> + size_t seg_size = min_t(size_t, iov_len, >> + folio_size - offset); >> + >> + res_bvec[bvec_idx].bv_page = src_bvec->bv_page; >> + res_bvec[bvec_idx].bv_offset = offset; >> + res_bvec[bvec_idx].bv_len = seg_size; > > Could just increment res_bvec to avoid the variable bvec_idx? I don't see the benefit. >> + for (i = 0; i < nr_iovs; i++) >> + max_segs += (iov[i].iov_len >> shift) + 2; > > Sees like this may overestimate a bit. I think something like this > would give the exact number of segments for each iovec? > (((u64)iov_base & folio_mask) + iov_len + folio_mask) >> folio_shift It's overestimated exactly to avoid a beast like this. -- Pavel Begunkov