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X-MS-Exchange-CrossTenant-Network-Message-Id: ae3ec116-1fec-42b3-86ed-08dd8c86f5e6 X-MS-Exchange-CrossTenant-AuthSource: BLAPR10MB5267.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2025 10:15:43.7553 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: h7WMmWxBdXvqLe+/E/BtMEXMZ6rlrCTGl9IjSki18d82lYZUjc4L6CyG4BXezHmdZnHKyTPWsQFdf6L3d6pdyg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR10MB5616 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-06_04,2025-05-05_01,2025-02-21_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 bulkscore=0 suspectscore=0 malwarescore=0 mlxscore=0 spamscore=0 mlxlogscore=999 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2504070000 definitions=main-2505060098 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTA2MDA5NyBTYWx0ZWRfX4ETDJUwsJY/i Mb3cJm9br2OdRexe7a5rdtXUsrBTwLvl2YPpl/Z5grBKmKIB03jWKLmQRXzOZUulczP/Qr+VE0S 7rkFhPVJn1okonn7vN+6Y2xNoDUYNmbK/7jcVw7qddlQaQzifYAjTGz0Wbak5zin9qWZi7XcFSt RQWW0dzYJn54FV926evwydRPBqrLGUatboEah4f84IxA9c+NY4/9XFawBbRjHLdMMuIMBZTMMgV SiEM+3B/X8FuAlkJU2On9C3kEsuVBILc0kdVKQ0hrvzjx/KYp1EBJr1bgZMhhishE9KJL9BlhgA d1fxoMezsuJSpGCtittzAtBxvDMiY8lSq5iU6P4Fh8cF+/DJNaG7hO7iftQtSwUX7y8wuJXChvr K2arpIhyG2jvs/VgiVPJVFSXsmtYE9ow/8RQmqM3JHCkIFdJncfQCS5oHG+fIryuewwRUQbJ X-Authority-Analysis: v=2.4 cv=ZoDtK87G c=1 sm=1 tr=0 ts=6819e158 b=1 cx=c_pps a=qoll8+KPOyaMroiJ2sR5sw==:117 a=qoll8+KPOyaMroiJ2sR5sw==:17 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=GoEa3M9JfhUA:10 a=pGLkceISAAAA:8 a=yPCof4ZbAAAA:8 a=VwQbUJbxAAAA:8 a=4tu2a3NUN02yIaBJ2e0A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 cc=ntf awl=host:13130 X-Proofpoint-ORIG-GUID: UlpuM4xHQkLdxQPq2RCEprwG1MuUgQuR X-Proofpoint-GUID: UlpuM4xHQkLdxQPq2RCEprwG1MuUgQuR On 05/05/2025 22:10, Andrii Nakryiko wrote: > On Fri, May 2, 2025 at 11:09 AM Alexei Starovoitov > wrote: >> >> On Fri, May 2, 2025 at 2:32 AM Alan Maguire wrote: >>> >>>> >>>> On the other hand, this seems to help to reduce duplication across many >>>> kernel modules. In my local test, I had 639 kernel module built. Overall >>>> .BTF sections size goes down from 41MB bytes down to 5MB (!), which is >>>> pretty impressive for such a straightforward piece of logic added. But >>>> it would be nice to validate independently just in case my bash and >>>> Python-fu is broken. >>>> >>>> Signed-off-by: Andrii Nakryiko >>> >>> Looks great! >>> >>> Reviewed-by: Alan Maguire >>> >>> Should have some numbers on the module size differences with this change >>> by Monday, had to dash before my build completed. >> >> I'm curious what BTF sizes you'll see. >> >> Sounds like dwarf has more cases of "same type but different id" >> than we expected. >> So existing workarounds are working only because we have very >> few modules that rely on proper dedup of kernel types. >> Beyond array/struct/ptrs, I wonder, what else is there. > > Well, turns out I screwed up the measurements. I thought that I used > libbpf version with Alan's patch applied as a baseline, but it turned > out it was libbpf without his patch. So all the measurements (41MB -> > 5MB) are actually due to Alan's identical pointers fix. My patches > have no effect on module BTF sizes (which is good and a bit more > sensible, I should have double checked before submitting). So, if we > are going to apply the patch, it's probably better to just drop that > paragraph. Or I can send v2 with an adjusted commit message, whatever > is better. > I did see some small changes, so the fact that you've added additional cases here definitely helps; with ~3000 modules built I got ~50Mb of module BTF in total both before and after the change, but comparing the results using latest pahole (with the pointer-specific fix) and your change (the more general fix) we do see some size reductions: $ find . -name '*.ko' -print |sort|xargs objdump -h --section=".BTF" > /tmp/modout.base $ awk '/file format/ { printf $1" " } / .BTF/ { print strtonum("0x" $3) }' /tmp/modout.base > /tmp/modout.base.sizes # rebuild pahole with Andrii's change $ rm vmlinux $ make -j$(nproc) $ find . -name '*.ko' -print |sort|xargs objdump -h --section=".BTF" > /tmp/modout.test $ awk '/file format/ { printf $1" " } /tmp/modout.test / .BTF/ { print strtonum("0x" $3) }' > /tmp/modout.test.sizes $ diff /tmp/modout.base.sizes /tmp/modout.test.sizes 198c198 < ./drivers/char/ipmi/ipmi_si.ko: 11575 --- > ./drivers/char/ipmi/ipmi_si.ko: 11539 1810c1810 < ./drivers/platform/x86/ideapad-laptop.ko: 7122 --- > ./drivers/platform/x86/ideapad-laptop.ko: 7086 1952c1952 < ./drivers/scsi/mpi3mr/mpi3mr.ko: 52625 --- > ./drivers/scsi/mpi3mr/mpi3mr.ko: 52589 So while numerically it isn't huge, it definitely validates the principle of making the identical type handling less specific to the cases we had encountered. If you want to resync libbpf github again I can update the submodule commit in pahole. Thanks! Alan