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| author |   Manfred Spraul <manfred@colorfullife.com> | 2021-06-30 18:57:18 -0700 |
|---|---|---|
| committer |   Linus Torvalds <torvalds@linux-foundation.org> | 2021-07-01 11:06:07 -0700 |
| commit | b869d5be0acf0e125e69adcffdca04000dc5b17c (patch) | |
| tree | 255499da3b1bf987add1b49fa73772f644553477 /ipc/util.h | |
| parent | ipc/sem.c: use READ_ONCE()/WRITE_ONCE() for use_global_lock (diff) | |
| download | linux-dev-b869d5be0acf0e125e69adcffdca04000dc5b17c.tar.xz linux-dev-b869d5be0acf0e125e69adcffdca04000dc5b17c.zip | |
ipc/util.c: use binary search for max_idx
If semctl(), msgctl() and shmctl() are called with IPC_INFO, SEM_INFO,
MSG_INFO or SHM_INFO, then the return value is the index of the highest
used index in the kernel's internal array recording information about all
SysV objects of the requested type for the current namespace. (This
information can be used with repeated ..._STAT or ..._STAT_ANY operations
to obtain information about all SysV objects on the system.)
There is a cache for this value. But when the cache needs up be updated,
then the highest used index is determined by looping over all possible
values. With the introduction of IPCMNI_EXTEND_SHIFT, this could be a
loop over 16 million entries. And due to /proc/sys/kernel/*next_id, the
index values do not need to be consecutive.
With <write 16000000 to msg_next_id>, msgget(), msgctl(,IPC_RMID) in a
loop, I have observed a performance increase of around factor 13000.
As there is no get_last() function for idr structures: Implement a
"get_last()" using a binary search.
As far as I see, ipc is the only user that needs get_last(), thus
implement it in ipc/util.c and not in a central location.
[akpm@linux-foundation.org: tweak comment, fix typo]
Link: https://lkml.kernel.org/r/20210425075208.11777-2-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: <1vier1@web.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc/util.h')
| -rw-r--r-- | ipc/util.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/ipc/util.h b/ipc/util.h index 5766c61aed0e..2dd7ce0416d8 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -145,6 +145,9 @@ int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flg); * ipc_get_maxidx - get the highest assigned index * @ids: ipc identifier set * + * The function returns the highest assigned index for @ids. The function + * doesn't scan the idr tree, it uses a cached value. + * * Called with ipc_ids.rwsem held for reading. */ static inline int ipc_get_maxidx(struct ipc_ids *ids) |