ksize(9) [centos man page]

KSIZE(9)						    Memory Management in Linux							  KSIZE(9)

NAME

       ksize - get the actual amount of memory allocated for a given object

SYNOPSIS

       size_t ksize(const void * objp);

ARGUMENTS

       objp
	   Pointer to the object

DESCRIPTION

       kmalloc may internally round up allocations and return more memory than requested.  ksize can be used to determine the actual amount of
       memory allocated. The caller may use this additional memory, even though a smaller amount of memory was initially specified with the
       kmalloc call. The caller must guarantee that objp points to a valid object previously allocated with either kmalloc or kmem_cache_alloc.
       The object must not be freed during the duration of the call.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014								  KSIZE(9)

BIO_ALLOC_BIOSET(9)						   The Linux VFS					       BIO_ALLOC_BIOSET(9)

NAME

       bio_alloc_bioset - allocate a bio for I/O

SYNOPSIS

       struct bio * bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set * bs);

ARGUMENTS

       gfp_mask
	   the GFP_ mask given to the slab allocator

       nr_iovecs
	   number of iovecs to pre-allocate

       bs
	   the bio_set to allocate from.

DESCRIPTION

       If bs is NULL, uses kmalloc to allocate the bio; else the allocation is backed by the bs's mempool.

       When bs is not NULL, if __GFP_WAIT is set then bio_alloc will always be able to allocate a bio. This is due to the mempool guarantees. To
       make this work, callers must never allocate more than 1 bio at a time from this pool. Callers that need to allocate more than 1 bio must
       always submit the previously allocated bio for IO before attempting to allocate a new one. Failure to do so can cause deadlocks under
       memory pressure.

       Note that when running under generic_make_request (i.e. any block driver), bios are not submitted until after you return - see the code in
       generic_make_request that converts recursion into iteration, to prevent stack overflows.

       This would normally mean allocating multiple bios under generic_make_request would be susceptible to deadlocks, but we have deadlock
       avoidance code that resubmits any blocked bios from a rescuer thread.

       However, we do not guarantee forward progress for allocations from other mempools. Doing multiple allocations from the same mempool under
       generic_make_request should be avoided - instead, use bio_set's front_pad for per bio allocations.

RETURNS

       Pointer to new bio on success, NULL on failure.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						       BIO_ALLOC_BIOSET(9)