Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752885Ab3C0NTz (ORCPT ); Wed, 27 Mar 2013 09:19:55 -0400 Received: from mail-oa0-f50.google.com ([209.85.219.50]:40767 "EHLO mail-oa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751671Ab3C0NSS (ORCPT ); Wed, 27 Mar 2013 09:18:18 -0400 From: Jeff Layton To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, tj@kernel.org Subject: [PATCH v1 1/6] idr: introduce idr_alloc_cyclic Date: Wed, 27 Mar 2013 09:18:03 -0400 Message-Id: <1364390288-30968-2-git-send-email-jlayton@redhat.com> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <1364390288-30968-1-git-send-email-jlayton@redhat.com> References: <1364390288-30968-1-git-send-email-jlayton@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4638 Lines: 139 Thus spake Tejun Heo: Ooh, BTW, the cyclic allocation is broken. It's prone to -ENOSPC after the first wraparound. There are several cyclic users in the kernel and I think it probably would be best to implement cyclic support in idr. This patch does that by adding new idr_alloc_cyclic function that such users in the kernel can use. With this, there's no need for a caller to keep track of the last value used as that's now tracked internally. This should prevent the ENOSPC problems that can hit when the "last allocated" counter exceeds INT_MAX. Later patches will convert existing cyclic users to the new interface. Cc: Tejun Heo Signed-off-by: Jeff Layton --- include/linux/idr.h | 10 +++++++++- lib/idr.c | 47 +++++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 52 insertions(+), 5 deletions(-) diff --git a/include/linux/idr.h b/include/linux/idr.h index 2640c7e..01752b1 100644 --- a/include/linux/idr.h +++ b/include/linux/idr.h @@ -42,6 +42,7 @@ struct idr { struct idr_layer *id_free; int layers; /* only valid w/o concurrent changes */ int id_free_cnt; + int cur; /* current pos for cyclic allocation */ spinlock_t lock; }; @@ -75,6 +76,7 @@ struct idr { void *idr_find_slowpath(struct idr *idp, int id); void idr_preload(gfp_t gfp_mask); int idr_alloc(struct idr *idp, void *ptr, int start, int end, gfp_t gfp_mask); +int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask); int idr_for_each(struct idr *idp, int (*fn)(int id, void *p, void *data), void *data); void *idr_get_next(struct idr *idp, int *nextid); @@ -82,7 +84,13 @@ void *idr_replace(struct idr *idp, void *ptr, int id); void idr_remove(struct idr *idp, int id); void idr_free(struct idr *idp, int id); void idr_destroy(struct idr *idp); -void idr_init(struct idr *idp); +void idr_init_cyclic(struct idr *idp, int start); + +static inline void +idr_init(struct idr *idp) +{ + idr_init_cyclic(idp, 0); +} /** * idr_preload_end - end preload section started with idr_preload() diff --git a/lib/idr.c b/lib/idr.c index 322e281..992f53f 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -495,6 +495,44 @@ int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask) } EXPORT_SYMBOL_GPL(idr_alloc); +/** + * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion + * @idr: the (initialized) idr + * @ptr: pointer to be associated with the new id + * @start: the minimum id (inclusive) + * @end: the maximum id (exclusive, <= 0 for max) + * @cur: ptr to current position in the range (typically, last allocated + 1) + * @gfp_mask: memory allocation flags + * + * Essentially the same as idr_alloc, but prefers to allocate progressively + * higher ids if it can. If the "cur" counter wraps, then it will start again + * at the "start" end of the range and allocate one that has already been used. + * + * Note that people using cyclic allocation to avoid premature reuse of an + * already-used ID may be in for a nasty surprise after idr->cur wraps. The + * IDR code is designed to avoid unnecessary allocations. If there is space + * in an existing layer that holds high IDs then it will return one of those + * instead of allocating a new layer at the bottom of the range. + */ +int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, + gfp_t gfp_mask) +{ + int id; + int cur = idr->cur; + + if (unlikely(start > cur)) + cur = start; + + id = idr_alloc(idr, ptr, cur, end, gfp_mask); + if (id == -ENOSPC) + id = idr_alloc(idr, ptr, start, end, gfp_mask); + + if (likely(id >= 0)) + idr->cur = id + 1; + return id; +} +EXPORT_SYMBOL(idr_alloc_cyclic); + static void idr_remove_warning(int id) { printk(KERN_WARNING @@ -831,19 +869,20 @@ void __init idr_init_cache(void) } /** - * idr_init - initialize idr handle + * idr_init_cyclic - initialize idr handle * @idp: idr handle + * @start: starting id value for cyclic users * * This function is use to set up the handle (@idp) that you will pass * to the rest of the functions. */ -void idr_init(struct idr *idp) +void idr_init_cyclic(struct idr *idp, int start) { memset(idp, 0, sizeof(struct idr)); spin_lock_init(&idp->lock); + idp->cur = start; } -EXPORT_SYMBOL(idr_init); - +EXPORT_SYMBOL(idr_init_cyclic); /** * DOC: IDA description -- 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/