On Thu, Mar 17, 2022 at 5:09 AM Andrew Morton akpm@linux-foundation.org wrote:
On Wed, 16 Mar 2022 11:41:37 +0800 Dong Aisheng dongas86@gmail.com wrote:
On Wed, Mar 16, 2022 at 6:58 AM Andrew Morton akpm@linux-foundation.org wrote:
On Tue, 15 Mar 2022 22:45:20 +0800 Dong Aisheng aisheng.dong@nxp.com wrote:
--- a/mm/cma.c +++ b/mm/cma.c
...
@@ -457,6 +458,16 @@ struct page *cma_alloc(struct cma *cma, unsigned long count, offset); if (bitmap_no >= bitmap_maxno) { spin_unlock_irq(&cma->lock);
pr_debug("%s(): alloc fail, retry loop %d\n", __func__, loop++);/** rescan as others may finish the memory migration* and quit if no available CMA memory found finally*/if (start) {schedule();start = 0;continue;} break;The schedule() is problematic. For a start, we'd normally use cond_resched() here, so we avoid calling the more expensive schedule() if we know it won't perform any action.
But cond_resched() is problematic if this thread has realtime scheduling policy and the process we're waiting on does not. One way to address that is to use an unconditional msleep(1), but that's still just a hack.
I think we can simply drop schedule() here during the second round of retry as the estimated delay may not be really needed.
That will simply cause a tight loop, so I'm obviously not understanding the proposal.
IIUC the original code is already a tight loop, isn't it? You could also see my observation, thousands of retries, in patch 2. The logic in this patch is just retry the original loop in case in case there's a false possive error return.
Or you mean infinite loop? The loop will break out when meet an non EBUSY error in alloc_contig_range().
BTW, the tight loop situation could be improved a lot by my patch 2.
And after Zi Yan's patchset [1] got merged, the situation could be further improved by retring in pageblock step. 1. [v7,0/5] Use pageblock_order for cma and alloc_contig_range alignment. - Patchwork (kernel.org)
So generally i wonder it seems still better than simply revert. Please fix me if i still missed something.
Regards Aisheng