linux-kernel - Re: [PATCH 1/1] mm/page_alloc: add scheduling point to free_unref_page

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Date:   Thu, 10 Mar 2022 10:11:43 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        wangjianxing <wangjianxing@...ngson.cn>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/page_alloc: add scheduling point to
 free_unref_page_list

On 3/10/22 04:29, Andrew Morton wrote:
> On Thu, 10 Mar 2022 10:48:41 +0800 wangjianxing <wangjianxing@...ngson.cn> wrote:
> 
>> 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();
>> 
> 
> None of this works with CONFIG_PREEMPTION=n.

Yeah I think we have at least two options.

1) check all callers, maybe realize all have enabled interrupts anyway,
rewrite the locking to only assume those

2) find out how long the tlb batches actually are and make them smaller