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

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Date:   Wed, 1 Apr 2020 16:00:27 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     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, david@...hat.com, jmorris@...ei.org,
        sashal@...nel.org
Subject: Re: [PATCH] mm: initialize deferred pages with interrupts enabled

On Wed, Apr 01, 2020 at 03:32:38PM -0400, 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

                                                                   not allowing
>    inter-node multi-threading.

     intra-node

...
> After:
> [    1.632580] node 0 initialised, 12051227 pages in 436ms

Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages")
Reported-by: Shile Zhang <shile.zhang@...ux.alibaba.com>

> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>

Freezing jiffies for a while during boot sounds like stable to me, so

Cc: <stable@...r.kernel.org>    [4.17.x+]


Can you please add a comment to mmzone.h above node_size_lock, something like

         * Must be held any time you expect node_start_pfn,
         * node_present_pages, node_spanned_pages or nr_zones to stay constant.
+        * Also synchronizes pgdat->first_deferred_pfn during deferred page
+        * init.
         ...
        spinlock_t node_size_lock;

> @@ -1854,18 +1859,6 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
>  		return false;
>  
>  	pgdat_resize_lock(pgdat, &flags);
> -
> -	/*
> -	 * If deferred pages have been initialized while we were waiting for
> -	 * the lock, return true, as the zone was grown.  The caller will retry
> -	 * this zone.  We won't return to this function since the caller also
> -	 * has this static branch.
> -	 */
> -	if (!static_branch_unlikely(&deferred_pages)) {
> -		pgdat_resize_unlock(pgdat, &flags);
> -		return true;
> -	}
> -

Huh, looks like this wasn't needed even before this change.


The rest looks fine.

Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>