On Wed, 12 Jun 2024 16:12:16 +0800 "zhai.he" <zhai.he@xxxxxxx> wrote:
> From: He Zhai <zhai.he@xxxxxxx>
(cc Barry & Christoph)
What was your reason for adding cc:stable to the email headers? Does
this address some serious problem? If so, please fully describe that
problem.
> In the current code logic, if the device-specified CMA memory
> allocation fails, memory will not be allocated from the default CMA area.
> This patch will use the default cma region when the device's
> specified CMA is not enough.
>
> In addition, the log level of allocation failure is changed to debug.
> Because these logs will be printed when memory allocation from the
> device specified CMA fails, but if the allocation fails, it will be
> allocated from the default cma area. It can easily mislead developers'
> judgment.
>
> ...
>
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -357,8 +357,13 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> /* CMA can be used only in the context which permits sleeping */
> if (!gfpflags_allow_blocking(gfp))
> return NULL;
> - if (dev->cma_area)
> - return cma_alloc_aligned(dev->cma_area, size, gfp);
> + if (dev->cma_area) {
> + struct page *page = NULL;
> +
> + page = cma_alloc_aligned(dev->cma_area, size, gfp);
> + if (page)
> + return page;
> + }
> if (size <= PAGE_SIZE)
> return NULL;
The dma_alloc_contiguous() kerneldoc should be updated for this.
The patch prompts the question "why does the device-specified CMA area
exist?". Why not always allocate from the global pool? If the
device-specified area exists to prevent one device from going crazy and
consuming too much contiguous memory, this patch violates that intent?
> @@ -406,6 +411,8 @@ void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
> if (dev->cma_area) {
> if (cma_release(dev->cma_area, page, count))
> return;
> + if (cma_release(dma_contiguous_default_area, page, count))
> + return;
> } else {
> /*
> * otherwise, page is from either per-numa cma or default cma
> diff --git a/mm/cma.c b/mm/cma.c
> index 3e9724716bad..6e12faf1bea7 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -495,8 +495,8 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> }
>
> if (ret && !no_warn) {
> - pr_err_ratelimited("%s: %s: alloc failed, req-size: %lu pages, ret: %d\n",
> - __func__, cma->name, count, ret);
> + pr_debug("%s: alloc failed, req-size: %lu pages, ret: %d, try to use default cma\n",
> + cma->name, count, ret);
> cma_debug_show_areas(cma);
> }
