Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/1] mm/page_alloc: add scheduling point to free_unref_page_list | From | wangjianxing <> | Date | Thu, 10 Mar 2022 10:48:41 +0800 |
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spin_lock will preempt_disable(), interrupt context will __irq_enter/local_bh_disable and also add preempt count with offset.
cond_resched check whether if preempt_count == 0 in first and won't schedule in previous context.
Is this right?
With another way, could we add some condition to avoid call cond_resched in interrupt context or spin_lock()?
+ if (preemptible()) + cond_resched();
On 03/10/2022 09:05 AM, Andrew Morton wrote: > On Tue, 8 Mar 2022 16:19:33 +0000 Matthew Wilcox <willy@infradead.org> wrote: > >> On Tue, Mar 01, 2022 at 08:38:25PM -0500, wangjianxing wrote: >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 3589febc6..1b96421c8 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -3479,6 +3479,9 @@ void free_unref_page_list(struct list_head *list) >>> */ >>> if (++batch_count == SWAP_CLUSTER_MAX) { >>> local_unlock_irqrestore(&pagesets.lock, flags); >>> + >>> + cond_resched(); >> This isn't safe. This path can be called from interrupt context >> (otherwise we'd be using local_unlock_irq() instead of irqrestore()). > What a shame it is that we don't document our interfaces :( > > I can't immediately find such callers, but I could imagine > put_pages_list() (which didn't document its interface this way either) > being called from IRQ. > > And drivers/iommu/dma-iommu.c:fq_ring_free() calls put_pages_list() > from inside spin_lock().
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