From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Linux-MM <linux-mm@kvack.org>,
Linux-RT-Users <linux-rt-users@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Chuck Lever <chuck.lever@oracle.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@kernel.org>,
Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH 02/11] mm/page_alloc: Convert per-cpu list protection to local_lock
Date: Fri, 9 Apr 2021 20:55:39 +0200 [thread overview]
Message-ID: <YHCjK8OOhmxTbKu0@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210409133256.GN3697@techsingularity.net>
On Fri, Apr 09, 2021 at 02:32:56PM +0100, Mel Gorman wrote:
> That said, there are some curious users already.
> fs/squashfs/decompressor_multi_percpu.c looks like it always uses the
> local_lock in CPU 0's per-cpu structure instead of stabilising a per-cpu
> pointer.
I'm not sure how you read that.
You're talking about this:
local_lock(&msblk->stream->lock);
right? Note that msblk->stream is a per-cpu pointer, so
&msblk->stream->lock is that same per-cpu pointer with an offset on.
The whole think relies on:
&per_cpu_ptr(msblk->stream, cpu)->lock == per_cpu_ptr(&msblk->stream->lock, cpu)
Which is true because the lhs:
(local_lock_t *)((msblk->stream + per_cpu_offset(cpu)) + offsetof(struct squashfs_stream, lock))
and the rhs:
(local_lock_t *)((msblk->stream + offsetof(struct squashfs_stream, lock)) + per_cpu_offset(cpu))
are identical, because addition is associative.
> drivers/block/zram/zcomp.c appears to do the same although for
> at least one of the zcomp_stream_get() callers, the CPU is pinned for
> other reasons (bit spin lock held). I think it happens to work anyway
> but it's weird and I'm not a fan.
Same thing.
next prev parent reply other threads:[~2021-04-09 18:57 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-07 20:24 [PATCH 0/11 v2] Use local_lock for pcp protection and reduce stat overhead Mel Gorman
2021-04-07 20:24 ` [PATCH 01/11] mm/page_alloc: Split per cpu page lists and zone stats Mel Gorman
2021-04-12 17:43 ` Vlastimil Babka
2021-04-13 13:27 ` Mel Gorman
2021-04-07 20:24 ` [PATCH 02/11] mm/page_alloc: Convert per-cpu list protection to local_lock Mel Gorman
2021-04-08 10:52 ` Peter Zijlstra
2021-04-08 17:42 ` Mel Gorman
2021-04-09 6:39 ` Peter Zijlstra
2021-04-09 7:59 ` Mel Gorman
2021-04-09 8:24 ` Peter Zijlstra
2021-04-09 13:32 ` Mel Gorman
2021-04-09 18:55 ` Peter Zijlstra [this message]
2021-04-12 11:56 ` Mel Gorman
2021-04-12 21:47 ` Thomas Gleixner
2021-04-13 16:52 ` Mel Gorman
2021-04-07 20:24 ` [PATCH 03/11] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove Mel Gorman
2021-04-07 20:24 ` [PATCH 04/11] mm/vmstat: Convert NUMA statistics to basic NUMA counters Mel Gorman
2021-04-14 12:56 ` Vlastimil Babka
2021-04-14 15:18 ` Mel Gorman
2021-04-14 15:56 ` Vlastimil Babka
2021-04-15 10:06 ` Mel Gorman
2021-04-07 20:24 ` [PATCH 05/11] mm/vmstat: Inline NUMA event counter updates Mel Gorman
2021-04-07 20:24 ` [PATCH 06/11] mm/page_alloc: Batch the accounting updates in the bulk allocator Mel Gorman
2021-04-07 20:24 ` [PATCH 07/11] mm/page_alloc: Reduce duration that IRQs are disabled for VM counters Mel Gorman
2021-04-07 20:24 ` [PATCH 08/11] mm/page_alloc: Remove duplicate checks if migratetype should be isolated Mel Gorman
2021-04-07 20:24 ` [PATCH 09/11] mm/page_alloc: Explicitly acquire the zone lock in __free_pages_ok Mel Gorman
2021-04-07 20:24 ` [PATCH 10/11] mm/page_alloc: Avoid conflating IRQs disabled with zone->lock Mel Gorman
2021-04-07 20:24 ` [PATCH 11/11] mm/page_alloc: Update PGFREE outside the zone lock in __free_pages_ok Mel Gorman
2021-04-08 10:56 ` [PATCH 0/11 v2] Use local_lock for pcp protection and reduce stat overhead Peter Zijlstra
2021-04-08 17:48 ` Mel Gorman
2021-04-14 13:39 [PATCH 0/11 v3] " Mel Gorman
2021-04-14 13:39 ` [PATCH 02/11] mm/page_alloc: Convert per-cpu list protection to local_lock Mel Gorman
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