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nvme-pci: derive and better document max segments limits

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Redefine the max segments and max integrity limits based on the limiting
factors.  This keeps exactly the same values for 4k PAGE_SIZE systems,
but increases the number of segments for larger page size as it properly
derives the scatterlist allocation based limit for them instead of
assuming a 4k PAGE_SIZE.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
This commit is contained in:
Christoph Hellwig
2025-05-20 05:34:27 +02:00
parent de65e64264
commit 414a4c93f1
1 changed files with 16 additions and 6 deletions
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drivers/nvme/host/pci.c
+16 -6
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@@ -35,8 +35,6 @@
#define SQ_SIZE(q) ((q)->q_depth << (q)->sqes)
#define CQ_SIZE(q) ((q)->q_depth * sizeof(struct nvme_completion))
#define SGES_PER_PAGE (NVME_CTRL_PAGE_SIZE / sizeof(struct nvme_sgl_desc))
/* Optimisation for I/Os between 4k and 128k */
#define NVME_SMALL_POOL_SIZE 256
@@ -45,10 +43,24 @@
* require an sg allocation that needs more than a page of data.
*/
#define NVME_MAX_KB_SZ 8192
#define NVME_MAX_SEGS 128
#define NVME_MAX_META_SEGS 15
#define NVME_MAX_NR_DESCRIPTORS 5
/*
* For data SGLs we support a single descriptors worth of SGL entries, but for
* now we also limit it to avoid an allocation larger than PAGE_SIZE for the
* scatterlist.
*/
#define NVME_MAX_SEGS \
min(NVME_CTRL_PAGE_SIZE / sizeof(struct nvme_sgl_desc), \
(PAGE_SIZE / sizeof(struct scatterlist)))
/*
* For metadata SGLs, only the small descriptor is supported, and the first
* entry is the segment descriptor, which for the data pointer sits in the SQE.
*/
#define NVME_MAX_META_SEGS \
((NVME_SMALL_POOL_SIZE / sizeof(struct nvme_sgl_desc)) - 1)
static int use_threaded_interrupts;
module_param(use_threaded_interrupts, int, 0444);
@@ -3829,8 +3841,6 @@ static int __init nvme_init(void)
BUILD_BUG_ON(sizeof(struct nvme_create_sq) != 64);
BUILD_BUG_ON(sizeof(struct nvme_delete_queue) != 64);
BUILD_BUG_ON(IRQ_AFFINITY_MAX_SETS < 2);
BUILD_BUG_ON(NVME_MAX_SEGS > SGES_PER_PAGE);
BUILD_BUG_ON(sizeof(struct scatterlist) * NVME_MAX_SEGS > PAGE_SIZE);
BUILD_BUG_ON(nvme_pci_npages_prp() > NVME_MAX_NR_DESCRIPTORS);
return pci_register_driver(&nvme_driver);