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 "fs/" 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_V5) that remove the ctl_table sentinel. We make the review process easier by chunking the commits into manageable pieces. Each chunk can be reviewed separately without noise from parallel sets. Sending the "fs/*" chunk now that the "drivers/" has been mostly reviewed [6]. After this and the "kernel/*" are reviewed we only have 2 more chunks ("net/*" and miscellaneous) to complete the sentinel removal. Hurray!!! 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 this patchset: * bloat-o-meter - The "yesall" config saves 1920 bytes [4] - The "tiny" config saves 576 bytes [5] * If you want to know how many bytes are saved after all the chunks are merged see [3] Base commit: tag: sysctl-6.7-rc1 (8b793bcda61f) 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: * E-mail threads that summarize the sentinel effort https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@xxxxxxxxxxxxxxxxxxxxxx/ https://lore.kernel.org/all/ZMFizKFkVxUFtSqa@xxxxxxxxxxxxxxxxxxxxxx/ * Replacing the register functions: https://lore.kernel.org/all/20230302204612.782387-1-mcgrof@xxxxxxxxxx/ https://lore.kernel.org/all/20230302202826.776286-1-mcgrof@xxxxxxxxxx/ * E-mail threads discussing prposal https://lore.kernel.org/all/20230321130908.6972-1-frank.li@xxxxxxxx https://lore.kernel.org/all/20220220060626.15885-1-tangmeng@xxxxxxxxxxxxx [3] 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 [7]) [4] add/remove: 0/0 grow/shrink: 0/30 up/down: 0/-1920 (-1920) Function old new delta xfs_table 1024 960 -64 vm_userfaultfd_table 128 64 -64 test_table_unregister 128 64 -64 test_table 576 512 -64 root_table 128 64 -64 pty_table 256 192 -64 ocfs2_nm_table 128 64 -64 ntfs_sysctls 128 64 -64 nlm_sysctls 448 384 -64 nfs_cb_sysctls 192 128 -64 nfs4_cb_sysctls 192 128 -64 namei_sysctls 320 256 -64 locks_sysctls 192 128 -64 inotify_table 256 192 -64 inodes_sysctls 192 128 -64 fsverity_sysctl_table 128 64 -64 fs_stat_sysctls 256 192 -64 fs_shared_sysctls 192 128 -64 fs_pipe_sysctls 256 192 -64 fs_namespace_sysctls 128 64 -64 fs_exec_sysctls 128 64 -64 fs_dqstats_table 576 512 -64 fs_dcache_sysctls 128 64 -64 fanotify_table 256 192 -64 epoll_table 128 64 -64 dnotify_sysctls 128 64 -64 coredump_sysctls 256 192 -64 coda_table 256 192 -64 cachefiles_sysctls 128 64 -64 aio_sysctls 192 128 -64 Total: Before=429912331, After=429910411, chg -0.00% [5] add/remove: 0/0 grow/shrink: 0/9 up/down: 0/-576 (-576) Function old new delta root_table 128 64 -64 namei_sysctls 320 256 -64 inodes_sysctls 192 128 -64 fs_stat_sysctls 256 192 -64 fs_shared_sysctls 192 128 -64 fs_pipe_sysctls 256 192 -64 fs_namespace_sysctls 128 64 -64 fs_exec_sysctls 128 64 -64 fs_dcache_sysctls 128 64 -64 Total: Before=1886645, After=1886069, chg -0.03% [6] https://lore.kernel.org/all/20231002-jag-sysctl_remove_empty_elem_drivers-v2-0-02dd0d46f71e@xxxxxxxxxxx [7] 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 + // + 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 --- Signed-off-by: Joel Granados <j.granados@xxxxxxxxxxx> --- Joel Granados (4): cachefiles: Remove the now superfluous sentinel element from ctl_table array aio: Remove the now superfluous sentinel elements from ctl_table array sysctl: Remove the now superfluous sentinel elements from ctl_table array coda: Remove the now superfluous sentinel elements from ctl_table array fs/aio.c | 1 - fs/cachefiles/error_inject.c | 1 - fs/coda/sysctl.c | 1 - fs/coredump.c | 1 - fs/dcache.c | 1 - fs/devpts/inode.c | 1 - fs/eventpoll.c | 1 - fs/exec.c | 1 - fs/file_table.c | 1 - fs/inode.c | 1 - fs/lockd/svc.c | 1 - fs/locks.c | 1 - fs/namei.c | 1 - fs/namespace.c | 1 - fs/nfs/nfs4sysctl.c | 1 - fs/nfs/sysctl.c | 1 - fs/notify/dnotify/dnotify.c | 1 - fs/notify/fanotify/fanotify_user.c | 1 - fs/notify/inotify/inotify_user.c | 1 - fs/ntfs/sysctl.c | 1 - fs/ocfs2/stackglue.c | 1 - fs/pipe.c | 1 - fs/proc/proc_sysctl.c | 1 - fs/quota/dquot.c | 1 - fs/sysctls.c | 1 - fs/userfaultfd.c | 1 - fs/verity/fsverity_private.h | 2 +- fs/verity/init.c | 8 +++++--- fs/xfs/xfs_sysctl.c | 2 -- lib/test_sysctl.c | 2 -- 30 files changed, 6 insertions(+), 34 deletions(-) --- base-commit: 8b793bcda61f6c3ed4f5b2ded7530ef6749580cb change-id: 20231107-jag-sysctl_remove_empty_elem_fs-dbdcf6581fbe Best regards, -- Joel Granados <j.granados@xxxxxxxxxxx>
