• Ming Lei's avatar
    scsi: lib/sg_pool.c: improve APIs for allocating sg pool · 4635873c
    Ming Lei authored
    sg_alloc_table_chained() currently allows the caller to provide one
    preallocated SGL and returns if the requested number isn't bigger than
    size of that SGL. This is used to inline an SGL for an IO request.
    
    However, scattergather code only allows that size of the 1st preallocated
    SGL to be SG_CHUNK_SIZE(128). This means a substantial amount of memory
    (4KB) is claimed for the SGL for each IO request. If the I/O is small, it
    would be prudent to allocate a smaller SGL.
    
    Introduce an extra parameter to sg_alloc_table_chained() and
    sg_free_table_chained() for specifying size of the preallocated SGL.
    
    Both __sg_free_table() and __sg_alloc_table() assume that each SGL has the
    same size except for the last one.  Change the code to allow both functions
    to accept a variable size for the 1st preallocated SGL.
    
    [mkp: attempted to clarify commit desc]
    
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Bart Van Assche <bvanassche@acm.org>
    Cc: Ewan D. Milne <emilne@redhat.com>
    Cc: Hannes Reinecke <hare@suse.com>
    Cc: Sagi Grimberg <sagi@grimberg.me>
    Cc: Chuck Lever <chuck.lever@oracle.com>
    Cc: netdev@vger.kernel.org
    Cc: linux-nvme@lists.infradead.org
    Suggested-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
    4635873c
scatterlist.c 25.2 KB