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]. Comments/feedback greatly appreciated 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> --- --- 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 hyper-v/azure: 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 | 3 +- drivers/cdrom/cdrom.c | 3 +- drivers/char/hpet.c | 3 +- drivers/char/ipmi/ipmi_poweroff.c | 3 +- drivers/char/random.c | 3 +- drivers/gpu/drm/i915/i915_perf.c | 3 +- drivers/hv/hv_common.c | 3 +- drivers/infiniband/core/iwcm.c | 3 +- drivers/infiniband/core/ucma.c | 3 +- drivers/macintosh/mac_hid.c | 3 +- drivers/md/md.c | 3 +- drivers/misc/sgi-xp/xpc_main.c | 6 ++-- drivers/net/vrf.c | 3 +- drivers/parport/procfs.c | 42 ++++++++++++--------------- drivers/scsi/scsi_sysctl.c | 3 +- drivers/scsi/sg.c | 3 +- drivers/tty/tty_io.c | 3 +- drivers/xen/balloon.c | 3 +- 18 files changed, 36 insertions(+), 60 deletions(-) --- base-commit: 0e945134b680040b8613e962f586d91b6d40292d change-id: 20230927-jag-sysctl_remove_empty_elem_drivers-f034962a0d8c Best regards, -- Joel Granados <j.granados@xxxxxxxxxxx>
