centos man page for idr_preload

IDR_PRELOAD(9)						  Basic Kernel Library Functions					    IDR_PRELOAD(9)

NAME
       idr_preload - preload for idr_alloc

SYNOPSIS
       void idr_preload(gfp_t gfp_mask);

ARGUMENTS
       gfp_mask
	   allocation mask to use for preloading

DESCRIPTION
       Preload per-cpu layer buffer for idr_alloc. Can only be used from process context and each idr_preload invocation should be matched with
       idr_preload_end. Note that preemption is disabled while preloaded.

       The first idr_alloc in the preloaded section can be treated as if it were invoked with gfp_mask used for preloading. This allows using more
       permissive allocation masks for idrs protected by spinlocks.

       For example, if idr_alloc below fails, the failure can be treated as if idr_alloc were called with GFP_KERNEL rather than GFP_NOWAIT.

       idr_preload(GFP_KERNEL); spin_lock(lock);

       id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT);

       spin_unlock(lock); idr_preload_end; if (id < 0) error;

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							    IDR_PRELOAD(9)