From b869d5be0acf0e125e69adcffdca04000dc5b17c Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Wed, 30 Jun 2021 18:57:18 -0700 Subject: 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 , 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 Acked-by: Davidlohr Bueso Cc: <1vier1@web.de> Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/util.c | 44 +++++++++++++++++++++++++++++++++++++++----- ipc/util.h | 3 +++ 2 files changed, 42 insertions(+), 5 deletions(-) diff --git a/ipc/util.c b/ipc/util.c index cfa0045e748d..0027e47626b7 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -64,6 +64,7 @@ #include #include #include +#include #include @@ -450,6 +451,41 @@ static void ipc_kht_remove(struct ipc_ids *ids, struct kern_ipc_perm *ipcp) ipc_kht_params); } +/** + * ipc_search_maxidx - search for the highest assigned index + * @ids: ipc identifier set + * @limit: known upper limit for highest assigned index + * + * The function determines the highest assigned index in @ids. It is intended + * to be called when ids->max_idx needs to be updated. + * Updating ids->max_idx is necessary when the current highest index ipc + * object is deleted. + * If no ipc object is allocated, then -1 is returned. + * + * ipc_ids.rwsem needs to be held by the caller. + */ +static int ipc_search_maxidx(struct ipc_ids *ids, int limit) +{ + int tmpidx; + int i; + int retval; + + i = ilog2(limit+1); + + retval = 0; + for (; i >= 0; i--) { + tmpidx = retval | (1<ipcs_idr, &tmpidx)) + retval |= (1<deleted = true; if (unlikely(idx == ids->max_idx)) { - do { - idx--; - if (idx == -1) - break; - } while (!idr_find(&ids->ipcs_idr, idx)); + idx = ids->max_idx-1; + if (idx >= 0) + idx = ipc_search_maxidx(ids, idx); ids->max_idx = idx; } } 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) -- cgit v1.2.3