linux-kernel - Re: [PATCH v2 2/2] mm: initialize deferred pages with interrupts enabled

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Date:   Thu, 2 Apr 2020 09:14:42 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        mhocko@...e.com, linux-mm@...ck.org, dan.j.williams@...el.com,
        shile.zhang@...ux.alibaba.com, daniel.m.jordan@...cle.com,
        ktkhai@...tuozzo.com, jmorris@...ei.org, sashal@...nel.org,
        vbabka@...e.cz
Subject: Re: [PATCH v2 2/2] mm: initialize deferred pages with interrupts
 enabled

On 02.04.20 00:57, Pavel Tatashin wrote:
> Initializing struct pages is a long task and keeping interrupts disabled
> for the duration of this operation introduces a number of problems.
> 
> 1. jiffies are not updated for long period of time, and thus incorrect time
>    is reported. See proposed solution and discussion here:
>    lkml/20200311123848.118638-1-shile.zhang@...ux.alibaba.com
> 2. It prevents farther improving deferred page initialization by allowing
>    intra-node multi-threading.
> 
> We are keeping interrupts disabled to solve a rather theoretical problem
> that was never observed in real world (See 3a2d7fa8a3d5).
> 
> Lets keep interrupts enabled. In case we ever encounter a scenario where
> an interrupt thread wants to allocate large amount of memory this early in
> boot we can deal with that by growing zone (see deferred_grow_zone()) by
> the needed amount before starting deferred_init_memmap() threads.
> 
> Before:
> [    1.232459] node 0 initialised, 12058412 pages in 1ms
> 
> After:
> [    1.632580] node 0 initialised, 12051227 pages in 436ms
> 
> Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages")
> Cc: stable@...r.kernel.org # 4.17+
> 

Can you please add my details about the use of cond_resched() fixing
detection of RCU stalls?

https://lore.kernel.org/linux-mm/20200401104156.11564-2-david@redhat.com/

In the meantime, I'll give these two patches a churn. Thanks


-- 
Thanks,

David / dhildenb