scsi_mod: add max_dma_memory and use_zone_normal params
PATCH 1/1 scsi_mod: add max_dma_memory and use_zone_normal params
For review and comment.
Patch adds two new module parameters to scsi_mod:
max_dma_memory=, maximum DMA pool size, in MB (default=32 -> 32MB) makes the hard-coded limit for the DMA pool size be adjustable. This
is necessary for systems with large numbers of disks seen (i.e. ~112 LUNs on a SAN as seen by a FC controller), where the size of the scsi_malloc() pool would consume all of ZONE_DMA, leaving none for other users. This lets a system admin set a limit on how much memory to use for the scsi_malloc() pool. If set too low, fewer outstanding commands can be issued at once, so it's only a performance issue.
use_zone_normal=, 1 if scsi_malloc() can safely use ZONE_NORMAL instead of ZONE_DMA By default, scsi_malloc() uses ZONE_DMA memory. On x86 and x86_64, ZONE_DMA is only 16MB, though if you've got a lot of disks, it could try to consume all of that. This lets scsi_malloc() use ZONE_NORMAL instead of ZONE_DMA, which of course is only safe if all your SCSI controllers are 64-bit-address-capable (most high-end cards today are). This flag lets you have lots more memory available to scsi_malloc() than would be available if it were forced to use only ZONE_DMA, and frees up the space it would otherwise have consumed from ZONE_DMA for other users.
Tested lightly on x86_64 on EM64T systems with 8GB RAM and up to 112 LUNs visible (14x8 paths, 28x4 paths, ...)
Thanks,
Matt
Signature · 65 lines
Matt Domsch
Software Architect
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com
===== drivers/scsi/scsi_dma.c 1.2 vs edited =====
--- 1.2/drivers/scsi/scsi_dma.c 2002-02-05 08:10:27 -06:00
+++ edited/drivers/scsi/scsi_dma.c 2005-03-18 11:31:11 -06:00
@@ -46,6 +46,29 @@ unsigned int scsi_dma_free_sectors = 0;
unsigned int scsi_need_isa_buffer = 0;
static unsigned char **dma_malloc_pages = NULL;
+static unsigned int max_dma_memory = 32; /* 32MB */
+MODULE_PARM(max_dma_memory, "l");
+MODULE_PARM_DESC(max_dma_memory, "maximum DMA pool size, in MB (default=32 -> 32MB)");
+
+
+/* This flag is unsafe under these conditions:
+ * - you've got a <64-bit addressable SCSI controller, >4GB RAM, and an architecture where ZONE_NORMAL
+ * extends above 4GB (any 64-bit architecture)
+ * or
+ * - you've got an old ISA card with host->unchecked_isa_dma=1
+ *
+ * This implies that it is really safe only with 64-bit addressable SCSI controllers
+ */
+static unsigned int use_zone_normal;
+MODULE_PARM(use_zone_normal, "i");
+MODULE_PARM_DESC(use_zone_normal, "1 if scsi_malloc() can safely use ZONE_NORMAL instead of ZONE_DMA");
+
+static inline unsigned int dma_gfp_flags()
+{
+ return use_zone_normal ? GFP_ATOMIC : GFP_ATOMIC | GFP_DMA;
+}
+
+
/*
* Function: scsi_malloc
*
@@ -287,7 +310,7 @@ void scsi_resize_dma_pool(void)
#endif
/* limit DMA memory to 32MB: */
- new_dma_sectors = (new_dma_sectors + 15) & 0xfff0;
+ new_dma_sectors = min(new_dma_sectors + 15, (max_dma_memory * 1024 * 2)) & 0xfffffff0;
/*
* We never shrink the buffers - this leads to
@@ -330,7 +353,7 @@ void scsi_resize_dma_pool(void)
for (i = dma_sectors / SECTORS_PER_PAGE;
i < new_dma_sectors / SECTORS_PER_PAGE; i++) {
new_dma_malloc_pages[i] = (unsigned char *)
- __get_free_pages(GFP_ATOMIC | GFP_DMA, 0);
+ __get_free_pages(dma_gfp_flags(), 0);
if (!new_dma_malloc_pages[i])
break;
}
@@ -430,7 +453,7 @@ int scsi_init_minimal_dma_pool(void)
if (dma_malloc_pages) {
memset(dma_malloc_pages, 0, size);
dma_malloc_pages[0] = (unsigned char *)
- __get_free_pages(GFP_ATOMIC | GFP_DMA, 0);
+ __get_free_pages(dma_gfp_flags(), 0);
if (dma_malloc_pages[0])
has_space = 1;
}