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Message-ID: <f39a7ebf-d67a-1535-271f-388d639cfa9a@I-love.SAKURA.ne.jp>
Date: Fri, 11 Aug 2023 00:35:03 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Michal Hocko <mhocko@...e.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Petr Mladek <pmladek@...e.com>, linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
"Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Ingo Molnar <mingo@...hat.com>,
John Ogness <john.ogness@...utronix.de>,
Mel Gorman <mgorman@...hsingularity.net>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2] mm/page_alloc: don't check zonelist_update_seq from
atomic allocations
On 2023/08/10 18:58, Tetsuo Handa wrote:
> If __build_all_zonelists() can run without being switched to other threads
> (except interrupt handlers), I consider that this approach works.
If there is no way to make sure that the section between
write_seqlock(&zonelist_update_seq) and write_sequnlock(&zonelist_update_seq)
runs without context switching (interrupts handlers are fine), something like
below could be used in order to keep
spin_lock(s->lock);
spin_unlock(s->lock);
away from seqprop_sequence() from atomic allocations. But I think that looses
the reason to replace read_seqbegin() with raw_seqcount_begin(); that will be
essentially the same with
https://lkml.kernel.org/r/dfdb9da6-ca8f-7a81-bfdd-d74b4c401f11@I-love.SAKURA.ne.jp .
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7d3460c7a480..f2f79caab2cf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3644,20 +3644,20 @@ EXPORT_SYMBOL_GPL(fs_reclaim_release);
*/
static DEFINE_SEQLOCK(zonelist_update_seq);
-static unsigned int zonelist_iter_begin(void)
+static unsigned int zonelist_iter_begin(gfp_t gfp)
{
- if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE))
- return read_seqbegin(&zonelist_update_seq);
+ if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE) && (gfp & __GFP_DIRECT_RECLAIM))
+ return data_race(raw_seqcount_begin(&zonelist_update_seq.seqcount));
return 0;
}
-static unsigned int check_retry_zonelist(unsigned int seq)
+static unsigned int check_retry_zonelist(gfp_t gfp, unsigned int seq)
{
- if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE))
- return read_seqretry(&zonelist_update_seq, seq);
+ if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE) && (gfp & __GFP_DIRECT_RECLAIM))
+ return data_race(read_seqcount_retry(&zonelist_update_seq.seqcount, seq));
- return seq;
+ return 0;
}
/* Perform direct synchronous page reclaim */
@@ -3968,7 +3968,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
no_progress_loops = 0;
compact_priority = DEF_COMPACT_PRIORITY;
cpuset_mems_cookie = read_mems_allowed_begin();
- zonelist_iter_cookie = zonelist_iter_begin();
+ zonelist_iter_cookie = zonelist_iter_begin(gfp_mask);
/*
* The fast path uses conservative alloc_flags to succeed only until
@@ -4146,7 +4146,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* a unnecessary OOM kill.
*/
if (check_retry_cpuset(cpuset_mems_cookie, ac) ||
- check_retry_zonelist(zonelist_iter_cookie))
+ check_retry_zonelist(gfp_mask, zonelist_iter_cookie))
goto restart;
/* Reclaim has failed us, start killing things */
@@ -4172,7 +4172,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* a unnecessary OOM kill.
*/
if (check_retry_cpuset(cpuset_mems_cookie, ac) ||
- check_retry_zonelist(zonelist_iter_cookie))
+ check_retry_zonelist(gfp_mask, zonelist_iter_cookie))
goto restart;
/*
@@ -5138,20 +5138,7 @@ static void __build_all_zonelists(void *data)
pg_data_t *self = data;
unsigned long flags;
- /*
- * Explicitly disable this CPU's interrupts before taking seqlock
- * to prevent any IRQ handler from calling into the page allocator
- * (e.g. GFP_ATOMIC) that could hit zonelist_iter_begin and livelock.
- */
- local_irq_save(flags);
- /*
- * Explicitly disable this CPU's synchronous printk() before taking
- * seqlock to prevent any printk() from trying to hold port->lock, for
- * tty_insert_flip_string_and_push_buffer() on other CPU might be
- * calling kmalloc(GFP_ATOMIC | __GFP_NOWARN) with port->lock held.
- */
- printk_deferred_enter();
- write_seqlock(&zonelist_update_seq);
+ write_seqlock_irqsave(&zonelist_update_seq, flags);
#ifdef CONFIG_NUMA
memset(node_load, 0, sizeof(node_load));
@@ -5188,9 +5175,7 @@ static void __build_all_zonelists(void *data)
#endif
}
- write_sequnlock(&zonelist_update_seq);
- printk_deferred_exit();
- local_irq_restore(flags);
+ write_sequnlock_irqrestore(&zonelist_update_seq, flags);
}
static noinline void __init
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