6 ms·

> Systemd is ~1.5MB - the loading time for emmc is 100ms Surely not all of systemd is faulted in immediately, is this really an issue?

amluto 7y ago
If you want just the important parts faulted in, you need to get the important parts into their own pages, preferably in order. I don’t know whether profile-guided linking is a thing.
- newnewpdro 7y ago
  On my long-running debian box, /lib/systemd/systemd is 1.1MiB in size. In /proc/1/smaps, I find the following executable mapping: 55aa05f89000-55aa06076000 r-xp 00000000 fd:01 1823 /lib/systemd/systemd Size: 948 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Rss: 752 kB Pss: 489 kB Shared_Clean: 504 kB Shared_Dirty: 0 kB Private_Clean: 248 kB Private_Dirty: 0 kB Referenced: 740 kB Anonymous: 0 kB LazyFree: 0 kB AnonHugePages: 0 kB ShmemPmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB Locked: 0 kB THPeligible: 0 VmFlags: rd ex mr mw me dw So it appears 740KiB has been referenced, 752KiB resident. There's also the read-only mapping: 55aa06076000-55aa0609b000 r--p 000ec000 fd:01 1823 /lib/systemd/systemd Size: 148 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Rss: 148 kB Pss: 74 kB Shared_Clean: 0 kB Shared_Dirty: 148 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 148 kB Anonymous: 148 kB LazyFree: 0 kB AnonHugePages: 0 kB ShmemPmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB Locked: 0 kB THPeligible: 0 VmFlags: rd mr mw me dw ac Another 148KiB, so 900KiB, a good chunk of the 1.1MiB - though this is with a substantial uptime. The really disgusting part is all the dependencies; `pmap 1` says 57MiB total, and there's not much anonymous memory to blame.
- PeCaN 7y ago
  PGO detects hot/cold functions and places them together¹ ², but I imagine whatever it needs on startup is probably not especially hot. …Though it might all be cold, which would have the same effect, actually. ― ¹ At least on GCC but I would be very surprised if clang doesn't also do this. ² You can also do this manually with __attribute__((hot)) and __attribute__((cold))
  - the8472 7y ago
    PGO may not be the right tool for this. Mozilla used custom instrumentation and linker scripts to achieve symbol ordering optimized for startup. https://web.archive.org/web/20100223202038/http://blog.mozilla.com/tglek/2010/02/19/teaching-ld-to-optimize-binaries-for-startup/ https://web.archive.org/web/20100223202038/http://blog.mozil...

amluto 7y ago

If you want just the important parts faulted in, you need to get the important parts into their own pages, preferably in order. I don’t know whether profile-guided linking is a thing.

newnewpdro 7y ago
On my long-running debian box, /lib/systemd/systemd is 1.1MiB in size. In /proc/1/smaps, I find the following executable mapping: 55aa05f89000-55aa06076000 r-xp 00000000 fd:01 1823 /lib/systemd/systemd Size: 948 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Rss: 752 kB Pss: 489 kB Shared_Clean: 504 kB Shared_Dirty: 0 kB Private_Clean: 248 kB Private_Dirty: 0 kB Referenced: 740 kB Anonymous: 0 kB LazyFree: 0 kB AnonHugePages: 0 kB ShmemPmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB Locked: 0 kB THPeligible: 0 VmFlags: rd ex mr mw me dw So it appears 740KiB has been referenced, 752KiB resident. There's also the read-only mapping: 55aa06076000-55aa0609b000 r--p 000ec000 fd:01 1823 /lib/systemd/systemd Size: 148 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Rss: 148 kB Pss: 74 kB Shared_Clean: 0 kB Shared_Dirty: 148 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 148 kB Anonymous: 148 kB LazyFree: 0 kB AnonHugePages: 0 kB ShmemPmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB Locked: 0 kB THPeligible: 0 VmFlags: rd mr mw me dw ac Another 148KiB, so 900KiB, a good chunk of the 1.1MiB - though this is with a substantial uptime. The really disgusting part is all the dependencies; `pmap 1` says 57MiB total, and there's not much anonymous memory to blame.
PeCaN 7y ago
PGO detects hot/cold functions and places them together¹ ², but I imagine whatever it needs on startup is probably not especially hot. …Though it might all be cold, which would have the same effect, actually. ― ¹ At least on GCC but I would be very surprised if clang doesn't also do this. ² You can also do this manually with __attribute__((hot)) and __attribute__((cold))
- the8472 7y ago
  PGO may not be the right tool for this. Mozilla used custom instrumentation and linker scripts to achieve symbol ordering optimized for startup. https://web.archive.org/web/20100223202038/http://blog.mozilla.com/tglek/2010/02/19/teaching-ld-to-optimize-binaries-for-startup/ https://web.archive.org/web/20100223202038/http://blog.mozil...