Re: [PATCH v2 00/15] sysctl: Remove sentinel elements from drivers

[Christophe Leroy]

Le 02/10/2023 à 10:55, Joel Granados via B4 Relay a écrit :
> From: Joel Granados <j.granados@xxxxxxxxxxx>
> 
> What?
> These commits remove the sentinel element (last empty element) from the
> sysctl arrays of all the files under the "drivers/" directory that use a
> sysctl array for registration. The merging of the preparation patches
> (in https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@xxxxxxxxxxxxxxxxxxxxxx/)
> to mainline allows us to just remove sentinel elements without changing
> behavior (more info here [1]).
> 
> These commits are part of a bigger set (here
> https://github.com/Joelgranados/linux/tree/tag/sysctl_remove_empty_elem_V4)
> that remove the ctl_table sentinel. Make the review process easier by
> chunking the commits into manageable pieces. Each chunk can be reviewed
> separately without noise from parallel sets.
> 
> Now that the architecture chunk has been mostly reviewed [6], we send
> the "drivers/" directory. Once this one is done, it will be follwed by
> "fs/*", "kernel/*", "net/*" and miscellaneous. The final set will remove
> the unneeded check for ->procname == NULL.
> 
> Why?
> By removing the sysctl sentinel elements we avoid kernel bloat as
> ctl_table arrays get moved out of kernel/sysctl.c into their own
> respective subsystems. This move was started long ago to avoid merge
> conflicts; the sentinel removal bit came after Mathew Wilcox suggested
> it to avoid bloating the kernel by one element as arrays moved out. This
> patchset will reduce the overall build time size of the kernel and run
> time memory bloat by about ~64 bytes per declared ctl_table array. I
> have consolidated some links that shed light on the history of this
> effort [2].
> 
> Testing:
> * Ran sysctl selftests (./tools/testing/selftests/sysctl/sysctl.sh)
> * Ran this through 0-day with no errors or warnings
> 
> Size saving after removing all sentinels:
>    These are the bytes that we save after removing all the sentinels
>    (this plus all the other chunks). I included them to get an idea of
>    how much memory we are talking about.
>      * bloat-o-meter:
>          - The "yesall" configuration results save 9158 bytes
>            https://lore.kernel.org/all/20230621091000.424843-1-j.granados@xxxxxxxxxxx/
>          - The "tiny" config + CONFIG_SYSCTL save 1215 bytes
>            https://lore.kernel.org/all/20230809105006.1198165-1-j.granados@xxxxxxxxxxx/
>      * memory usage:
>          In memory savings are measured to be 7296 bytes. (here is how to
>          measure [3])
> 
> Size saving after this patchset:
>      * bloat-o-meter
>          - The "yesall" config saves 2432 bytes [4]
>          - The "tiny" config saves 64 bytes [5]
>      * memory usage:
>          In this case there were no bytes saved because I do not have any
>          of the drivers in the patch. To measure it comment the printk in
>          `new_dir` and uncomment the if conditional in `new_links` [3].
> 
> ---
> Changes in v2:
> - Left the dangling comma in the ctl_table arrays.
> - Link to v1: https://lore.kernel.org/r/20230928-jag-sysctl_remove_empty_elem_drivers-v1-0-e59120fca9f9@xxxxxxxxxxx
> 
> Comments/feedback greatly appreciated

Same problem on powerpc CI tests, all boot target failed, most of them 
with similar OOPS, see 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20231002-jag-sysctl_remove_empty_elem_drivers-v2-15-02dd0d46f71e@xxxxxxxxxxx/

What is strange is that I pushed your series into my github account, and 
got no failure, see https://github.com/chleroy/linux/actions/runs/6378951278

Christophe

> 
> Best
> 
> Joel
> 
> [1]
> We are able to remove a sentinel table without behavioral change by
> introducing a table_size argument in the same place where procname is
> checked for NULL. The idea is for it to keep stopping when it hits
> ->procname == NULL, while the sentinel is still present. And when the
> sentinel is removed, it will stop on the table_size. You can go to
> (https://lore.kernel.org/all/20230809105006.1198165-1-j.granados@xxxxxxxxxxx/)
> for more information.
> 
> [2]
> Links Related to the ctl_table sentinel removal:
> * Good summary from Luis sent with the "pull request" for the
>    preparation patches.
>    https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@xxxxxxxxxxxxxxxxxxxxxx/
> * Another very good summary from Luis.
>    https://lore.kernel.org/all/ZMFizKFkVxUFtSqa@xxxxxxxxxxxxxxxxxxxxxx/
> * This is a patch set that replaces register_sysctl_table with register_sysctl
>    https://lore.kernel.org/all/20230302204612.782387-1-mcgrof@xxxxxxxxxx/
> * Patch set to deprecate register_sysctl_paths()
>    https://lore.kernel.org/all/20230302202826.776286-1-mcgrof@xxxxxxxxxx/
> * Here there is an explicit expectation for the removal of the sentinel element.
>    https://lore.kernel.org/all/20230321130908.6972-1-frank.li@xxxxxxxx
> * The "ARRAY_SIZE" approach was mentioned (proposed?) in this thread
>    https://lore.kernel.org/all/20220220060626.15885-1-tangmeng@xxxxxxxxxxxxx
> 
> [3]
> To measure the in memory savings apply this on top of this patchset.
> 
> "
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index c88854df0b62..e0073a627bac 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -976,6 +976,8 @@ static struct ctl_dir *new_dir(struct ctl_table_set *set,
>          table[0].procname = new_name;
>          table[0].mode = S_IFDIR|S_IRUGO|S_IXUGO;
>          init_header(&new->header, set->dir.header.root, set, node, table, 1);
> +       // Counts additional sentinel used for each new dir.
> +       printk("%ld sysctl saved mem kzalloc \n", sizeof(struct ctl_table));
> 
>          return new;
>   }
> @@ -1199,6 +1201,9 @@ static struct ctl_table_header *new_links(struct ctl_dir *dir, struct ctl_table_
>                  link_name += len;
>                  link++;
>          }
> +       // Counts additional sentinel used for each new registration
> +       //if ((head->ctl_table + head->ctl_table_size)->procname)
> +               printk("%ld sysctl saved mem kzalloc \n", sizeof(struct ctl_table));
>          init_header(links, dir->header.root, dir->header.set, node, link_table,
>                      head->ctl_table_size);
>          links->nreg = nr_entries;
> "
> and then run the following bash script in the kernel:
> 
> accum=0
> for n in $(dmesg | grep kzalloc | awk '{print $3}') ; do
>      echo $n
>      accum=$(calc "$accum + $n")
> done
> echo $accum
> 
> [4]
> add/remove: 0/0 grow/shrink: 0/21 up/down: 0/-2432 (-2432)
> Function                                     old     new   delta
> xpc_sys_xpc_hb                               192     128     -64
> xpc_sys_xpc                                  128      64     -64
> vrf_table                                    128      64     -64
> ucma_ctl_table                               128      64     -64
> tty_table                                    192     128     -64
> sg_sysctls                                   128      64     -64
> scsi_table                                   128      64     -64
> random_table                                 448     384     -64
> raid_table                                   192     128     -64
> oa_table                                     192     128     -64
> mac_hid_files                                256     192     -64
> iwcm_ctl_table                               128      64     -64
> ipmi_table                                   128      64     -64
> hv_ctl_table                                 128      64     -64
> hpet_table                                   128      64     -64
> firmware_config_table                        192     128     -64
> cdrom_table                                  448     384     -64
> balloon_table                                128      64     -64
> parport_sysctl_template                      912     720    -192
> parport_default_sysctl_table                 584     136    -448
> parport_device_sysctl_template               776     136    -640
> Total: Before=429940038, After=429937606, chg -0.00%
> 
> [5]
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-64 (-64)
> Function                                     old     new   delta
> random_table                                 448     384     -64
> Total: Before=1885527, After=1885463, chg -0.00%
> 
> [6] https://lore.kernel.org/all/20230913-jag-sysctl_remove_empty_elem_arch-v2-0-d1bd13a29bae@xxxxxxxxxxx/
> 
> Signed-off-by: Joel Granados <j.granados@xxxxxxxxxxx>
> 
> To: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> To: willy@xxxxxxxxxxxxx
> To: josh@xxxxxxxxxxxxxxxx
> To: Kees Cook <keescook@xxxxxxxxxxxx>
> To: Phillip Potter <phil@xxxxxxxxxxxxxxxx>
> To: Clemens Ladisch <clemens@xxxxxxxxxx>
> To: Arnd Bergmann <arnd@xxxxxxxx>
> To: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> To: Juergen Gross <jgross@xxxxxxxx>
> To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> To: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> To: Jiri Slaby <jirislaby@xxxxxxxxxx>
> To: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxx>
> To: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
> To: Doug Gilbert <dgilbert@xxxxxxxxxxxx>
> To: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
> To: Jason Gunthorpe <jgg@xxxxxxxx>
> To: Leon Romanovsky <leon@xxxxxxxxxx>
> To: Corey Minyard <minyard@xxxxxxx>
> To: Theodore Ts'o <tytso@xxxxxxx>
> To: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
> To: David Ahern <dsahern@xxxxxxxxxx>
> To: "David S. Miller" <davem@xxxxxxxxxxxxx>
> To: Eric Dumazet <edumazet@xxxxxxxxxx>
> To: Jakub Kicinski <kuba@xxxxxxxxxx>
> To: Paolo Abeni <pabeni@xxxxxxxxxx>
> To: Robin Holt <robinmholt@xxxxxxxxx>
> To: Steve Wahl <steve.wahl@xxxxxxx>
> To: Russ Weight <russell.h.weight@xxxxxxxxx>
> To: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> To: Song Liu <song@xxxxxxxxxx>
> To: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> To: Wei Liu <wei.liu@xxxxxxxxxx>
> To: Dexuan Cui <decui@xxxxxxxxxxxxx>
> To: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> To: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> To: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> To: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> To: David Airlie <airlied@xxxxxxxxx>
> To: Daniel Vetter <daniel@xxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: linux-serial@xxxxxxxxxxxxxxx
> Cc: linux-scsi@xxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-rdma@xxxxxxxxxxxxxxx
> Cc: openipmi-developer@xxxxxxxxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-raid@xxxxxxxxxxxxxxx
> Cc: linux-hyperv@xxxxxxxxxxxxxxx
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> 
> ---
> 
> ---
> Joel Granados (15):
>        cdrom: Remove now superfluous sentinel element from ctl_table array
>        hpet: Remove now superfluous sentinel element from ctl_table array
>        xen: Remove now superfluous sentinel element from ctl_table array
>        tty: Remove now superfluous sentinel element from ctl_table array
>        scsi: Remove now superfluous sentinel element from ctl_table array
>        parport: Remove the now superfluous sentinel element from ctl_table array
>        macintosh: Remove the now superfluous sentinel element from ctl_table array
>        infiniband: Remove the now superfluous sentinel element from ctl_table array
>        char-misc: Remove the now superfluous sentinel element from ctl_table array
>        vrf: Remove the now superfluous sentinel element from ctl_table array
>        sgi-xp: Remove the now superfluous sentinel element from ctl_table array
>        fw loader: Remove the now superfluous sentinel element from ctl_table array
>        raid: Remove now superfluous sentinel element from ctl_table array
>        Drivers: hv: Remove now superfluous sentinel element from ctl_table array
>        intel drm: Remove now superfluous sentinel element from ctl_table array
> 
>   drivers/base/firmware_loader/fallback_table.c |  1 -
>   drivers/cdrom/cdrom.c                         |  1 -
>   drivers/char/hpet.c                           |  1 -
>   drivers/char/ipmi/ipmi_poweroff.c             |  1 -
>   drivers/char/random.c                         |  1 -
>   drivers/gpu/drm/i915/i915_perf.c              |  1 -
>   drivers/hv/hv_common.c                        |  1 -
>   drivers/infiniband/core/iwcm.c                |  1 -
>   drivers/infiniband/core/ucma.c                |  1 -
>   drivers/macintosh/mac_hid.c                   |  1 -
>   drivers/md/md.c                               |  1 -
>   drivers/misc/sgi-xp/xpc_main.c                |  2 --
>   drivers/net/vrf.c                             |  1 -
>   drivers/parport/procfs.c                      | 28 +++++++++++----------------
>   drivers/scsi/scsi_sysctl.c                    |  1 -
>   drivers/scsi/sg.c                             |  1 -
>   drivers/tty/tty_io.c                          |  1 -
>   drivers/xen/balloon.c                         |  1 -
>   18 files changed, 11 insertions(+), 35 deletions(-)
> ---
> base-commit: 0e945134b680040b8613e962f586d91b6d40292d
> change-id: 20230927-jag-sysctl_remove_empty_elem_drivers-f034962a0d8c
> 
> Best regards,