linux-kernel - Re: [PATCH v3 1/1] mm: initialize pages on demand during boot

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Message-Id: <20180209123615.4715623481fa07f7b14fd447@linux-foundation.org>
Date:   Fri, 9 Feb 2018 12:36:15 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        m.mizuma@...fujitsu.com, mhocko@...e.com, catalin.marinas@....com,
        takahiro.akashi@...aro.org, gi-oh.kim@...fitbricks.com,
        heiko.carstens@...ibm.com, baiyaowei@...s.chinamobile.com,
        richard.weiyang@...il.com, paul.burton@...s.com,
        miles.chen@...iatek.com, vbabka@...e.cz, mgorman@...e.de,
        hannes@...xchg.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3 1/1] mm: initialize pages on demand during boot

On Fri,  9 Feb 2018 14:22:16 -0500 Pavel Tatashin <pasha.tatashin@...cle.com> wrote:

> Deferred page initialization allows the boot cpu to initialize a small
> subset of the system's pages early in boot, with other cpus doing the rest
> later on.
> 
> It is, however, problematic to know how many pages the kernel needs during
> boot.  Different modules and kernel parameters may change the requirement,
> so the boot cpu either initializes too many pages or runs out of memory.
> 
> To fix that, initialize early pages on demand.  This ensures the kernel
> does the minimum amount of work to initialize pages during boot and leaves
> the rest to be divided in the multithreaded initialization path
> (deferred_init_memmap).
> 
> The on-demand code is permanently disabled using static branching once
> deferred pages are initialized.  After the static branch is changed to
> false, the overhead is up-to two branch-always instructions if the zone
> watermark check fails or if rmqueue fails.

lgtm, I'll toss it in for some testing.

A couple of tweaks:

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm-initialize-pages-on-demand-during-boot-fix

fix typo in comment, make deferred_pages static

Cc: Pavel Tatashin <pasha.tatashin@...cle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/page_alloc.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -puN include/linux/memblock.h~mm-initialize-pages-on-demand-during-boot-fix include/linux/memblock.h
diff -puN mm/memblock.c~mm-initialize-pages-on-demand-during-boot-fix mm/memblock.c
diff -puN mm/page_alloc.c~mm-initialize-pages-on-demand-during-boot-fix mm/page_alloc.c
--- a/mm/page_alloc.c~mm-initialize-pages-on-demand-during-boot-fix
+++ a/mm/page_alloc.c
@@ -1568,14 +1568,14 @@ static int __init deferred_init_memmap(v
 }
 
 /*
- * This lock grantees that only one thread at a time is allowed to grow zones
+ * This lock guarantees that only one thread at a time is allowed to grow zones
  * (decrease number of deferred pages).
  * Protects first_deferred_pfn field in all zones during early boot before
  * deferred pages are initialized.  Deferred pages are initialized in
  * page_alloc_init_late() soon after smp_init() is complete.
  */
 static __initdata DEFINE_SPINLOCK(deferred_zone_grow_lock);
-DEFINE_STATIC_KEY_TRUE(deferred_pages);
+static DEFINE_STATIC_KEY_TRUE(deferred_pages);
 
 /*
  * If this zone has deferred pages, try to grow it by initializing enough
_