| Message ID | 20230118225447.2809787-2-bvanassche@acm.org |
|---|---|
| State | New |
| Headers | show |
| Series | Add support for segments smaller than one page | expand |
On 1/18/23 15:02, Jens Axboe wrote: > On 1/18/23 3:54 PM, Bart Van Assche wrote: >> Prepare for introducing support for segments smaller than the page size >> by introducing the request queue flag QUEUE_FLAG_SUB_PAGE_SEGMENTS. >> Introduce CONFIG_BLK_SUB_PAGE_SEGMENTS to prevent that performance of >> block drivers that support segments >= PAGE_SIZE would be affected. >> >> Cc: Christoph Hellwig <hch@lst.de> >> Cc: Ming Lei <ming.lei@redhat.com> >> Cc: Keith Busch <kbusch@kernel.org> >> Signed-off-by: Bart Van Assche <bvanassche@acm.org> >> --- >> block/Kconfig | 9 +++++++++ >> include/linux/blkdev.h | 7 +++++++ >> 2 files changed, 16 insertions(+) >> >> diff --git a/block/Kconfig b/block/Kconfig >> index 5d9d9c84d516..e85061d2175b 100644 >> --- a/block/Kconfig >> +++ b/block/Kconfig >> @@ -35,6 +35,15 @@ config BLOCK_LEGACY_AUTOLOAD >> created on demand, but scripts that manually create device nodes and >> then call losetup might rely on this behavior. >> >> +config BLK_SUB_PAGE_SEGMENTS >> + bool "Support segments smaller than the page size" >> + default n >> + help >> + Most storage controllers support DMA segments larger than the typical >> + size of a virtual memory page. Some embedded controllers only support >> + DMA segments smaller than the page size. Enable this option to support >> + such controllers. > > This should not be a visible option at all, affected drivers should just > select it. Hi Jens, If CONFIG_BLK_SUB_PAGE_SEGMENTS is made invisible, how should this option be enabled for the scsi_debug and null_blk drivers? Adding "select BLK_SUB_PAGE_SEGMENTS" to the Kconfig section of these drivers would have the unfortunate side effect that enabling either driver would make all block drivers slower. How about making sub-page segment support configurable for the scsi_debug and null_blk drivers only? That would allow kernel developers who want to test the sub-page segment support to enable this functionality without making e.g. distro kernels slower. Thanks, Bart.
diff --git a/block/Kconfig b/block/Kconfig index 5d9d9c84d516..e85061d2175b 100644 --- a/block/Kconfig +++ b/block/Kconfig @@ -35,6 +35,15 @@ config BLOCK_LEGACY_AUTOLOAD created on demand, but scripts that manually create device nodes and then call losetup might rely on this behavior. +config BLK_SUB_PAGE_SEGMENTS + bool "Support segments smaller than the page size" + default n + help + Most storage controllers support DMA segments larger than the typical + size of a virtual memory page. Some embedded controllers only support + DMA segments smaller than the page size. Enable this option to support + such controllers. + config BLK_RQ_ALLOC_TIME bool diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 89f51d68c68a..6cbb22fb93ee 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -547,6 +547,7 @@ struct request_queue { /* Keep blk_queue_flag_name[] in sync with the definitions below */ #define QUEUE_FLAG_STOPPED 0 /* queue is stopped */ #define QUEUE_FLAG_DYING 1 /* queue being torn down */ +#define QUEUE_FLAG_SUB_PAGE_SEGMENTS 2 /* segments smaller than one page */ #define QUEUE_FLAG_NOMERGES 3 /* disable merge attempts */ #define QUEUE_FLAG_SAME_COMP 4 /* complete on same CPU-group */ #define QUEUE_FLAG_FAIL_IO 5 /* fake timeout */ @@ -613,6 +614,12 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q); #define blk_queue_sq_sched(q) test_bit(QUEUE_FLAG_SQ_SCHED, &(q)->queue_flags) #define blk_queue_skip_tagset_quiesce(q) \ test_bit(QUEUE_FLAG_SKIP_TAGSET_QUIESCE, &(q)->queue_flags) +#ifdef CONFIG_BLK_SUB_PAGE_SEGMENTS +#define blk_queue_sub_page_segments(q) \ + test_bit(QUEUE_FLAG_SUB_PAGE_SEGMENTS, &(q)->queue_flags) +#else +#define blk_queue_sub_page_segments(q) false +#endif extern void blk_set_pm_only(struct request_queue *q); extern void blk_clear_pm_only(struct request_queue *q);
Prepare for introducing support for segments smaller than the page size by introducing the request queue flag QUEUE_FLAG_SUB_PAGE_SEGMENTS. Introduce CONFIG_BLK_SUB_PAGE_SEGMENTS to prevent that performance of block drivers that support segments >= PAGE_SIZE would be affected. Cc: Christoph Hellwig <hch@lst.de> Cc: Ming Lei <ming.lei@redhat.com> Cc: Keith Busch <kbusch@kernel.org> Signed-off-by: Bart Van Assche <bvanassche@acm.org> --- block/Kconfig | 9 +++++++++ include/linux/blkdev.h | 7 +++++++ 2 files changed, 16 insertions(+)