Messages in this thread | | | From | "Tang, Feng" <> | Subject | Re: [PATCH] CMA: Don't return a valid cma for non-cma dev | Date | Fri, 31 Jul 2015 02:51:11 +0000 |
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Hi Michal Nazarewicz,
Thanks for the review.
On Thu, 2015-07-30 at 15:59 +0200, Michal Nazarewicz wrote: > On Thu, Jul 30 2015, Feng Tang wrote: > > When system(one x86 soc) boot, we saw many normal dma allocation requests > > goes to cma area. The call chain is > > dma_generic_alloc_coherent > > dma_alloc_from_contiguous -- arch/x86/kernel/pci-dma.c > > cma_alloc(dev_get_cma_area(dev), count, align) > > > > Current dev_get_cma_area() will return a valid "cma" anyway. Then all > > these requests will be taken as valid cma request, and get pages from > > cma area, which has 2 problems: > > 1. make the cma area fragmented > > 2. confuse the cma reservation, usually cma memory size is set according > > to the expectation of system scenario, these unexpected requests > > will affect the designed cma usage. > > > > So this patch will enforce the judgement, and only return valid "cma" > > for real cma user, thus make normal user like IO device driver not > > abuse cma reserved region. > > Just don’t set dma_contiguous_default_area. This patch defeats the > purpose of a *default* area.
Yes! This is exactly what I tried when I first saw this problem, but this failed as there 2 places inside drivers/base/dma-contiguous.c which set the dma_contiguous_default_area
1) void __init dma_contiguous_reserve(phys_addr_t limit) { .... dma_contiguous_reserve_area(selected_size, selected_base, selected_limit, &dma_contiguous_default_area, fixed); .... }
2) static int __init rmem_cma_setup(struct reserved_mem *rmem) { ... if (of_get_flat_dt_prop(node, "linux,cma-default", NULL)) dma_contiguous_set_default(cma); ... }
Are you suggesting me to remove them?
Thanks, Feng
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