mempool_alloc(9) [centos man page]

MEMPOOL_ALLOC(9)					    Memory Management in Linux						  MEMPOOL_ALLOC(9)

NAME

       mempool_alloc - allocate an element from a specific memory pool

SYNOPSIS

       void * mempool_alloc(mempool_t * pool, gfp_t gfp_mask);

ARGUMENTS

       pool
	   pointer to the memory pool which was allocated via mempool_create.

       gfp_mask
	   the usual allocation bitmask.

DESCRIPTION

       this function only sleeps if the alloc_fn function sleeps or returns NULL. Note that due to preallocation, this function *never* fails when
       called from process contexts. (it might fail if called from an IRQ context.)

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014							  MEMPOOL_ALLOC(9)

BLK_MAKE_REQUEST(9)						   Block Devices					       BLK_MAKE_REQUEST(9)

NAME

       blk_make_request - given a bio, allocate a corresponding struct request.

SYNOPSIS

       struct request * blk_make_request(struct request_queue * q, struct bio * bio, gfp_t gfp_mask);

ARGUMENTS

       q
	   target request queue

       bio
	   The bio describing the memory mappings that will be submitted for IO. It may be a chained-bio properly constructed by block/bio layer.

       gfp_mask
	   gfp flags to be used for memory allocation

DESCRIPTION

       blk_make_request is the parallel of generic_make_request for BLOCK_PC type commands. Where the struct request needs to be farther
       initialized by the caller. It is passed a struct bio, which describes the memory info of the I/O transfer.

       The caller of blk_make_request must make sure that bi_io_vec are set to describe the memory buffers. That bio_data_dir will return the
       needed direction of the request. (And all bio's in the passed bio-chain are properly set accordingly)

       If called under none-sleepable conditions, mapped bio buffers must not need bouncing, by calling the appropriate masked or flagged
       allocator, suitable for the target device. Otherwise the call to blk_queue_bounce will BUG.

WARNING

       When allocating/cloning a bio-chain, careful consideration should be given to how you allocate bios. In particular, you cannot use
       __GFP_WAIT for anything but the first bio in the chain. Otherwise you risk waiting for IO completion of a bio that hasn't been submitted
       yet, thus resulting in a deadlock. Alternatively bios should be allocated using bio_kmalloc instead of bio_alloc, as that avoids the
       mempool deadlock. If possible a big IO should be split into smaller parts when allocation fails. Partial allocation should not be an error,
       or you risk a live-lock.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						       BLK_MAKE_REQUEST(9)