From: Nicolas Pitre <nicolas.pitre@linaro.org> To: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info Date: Tue, 3 Oct 2017 18:29:49 -0400 (EDT) [thread overview] Message-ID: <nycvar.YSQ.7.76.1710031731130.5407@knanqh.ubzr> (raw) In-Reply-To: <20171003210540.GM3301751@devbig577.frc2.facebook.com> On Tue, 3 Oct 2017, Tejun Heo wrote: > On Tue, Oct 03, 2017 at 04:57:44PM -0400, Nicolas Pitre wrote: > > This can be much smaller than a page on very small memory systems. > > Always rounding up the size to a page is wasteful in that case, and > > required alignment is smaller than the memblock default. Let's round > > things up to a page size only when the actual size is >= page size, and > > then it makes sense to page-align for a nicer allocation pattern. > > Isn't that a temporary area which gets freed later during boot? Hmmm... It may get freed through 3 different paths where 2 of them are error paths. What looks like a non-error path is in pcpu_embed_first_chunk() called from setup_per_cpu_areas(). But there are two versions of setup_per_cpu_areas(): one for SMP and one for !SMP. And the !SMP case never calls pcpu_free_alloc_info() currently. I'm not sure i understand that code fully, but maybe the following patch could be a better fit: ----- >8 Subject: [PATCH] percpu: don't forget to free the temporary struct pcpu_alloc_info Unlike the SMP case, the !SMP case does not free the memory for struct pcpu_alloc_info allocated in setup_per_cpu_areas(). And to give it a chance of being reused by the page allocator later, align it to a page boundary just like its size. Signed-off-by: Nicolas Pitre <nico@linaro.org> diff --git a/mm/percpu.c b/mm/percpu.c index 434844415d..caab63375b 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1416,7 +1416,7 @@ struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups, __alignof__(ai->groups[0].cpu_map[0])); ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]); - ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), 0); + ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), PAGE_SIZE); if (!ptr) return NULL; ai = ptr; @@ -2295,6 +2295,7 @@ void __init setup_per_cpu_areas(void) if (pcpu_setup_first_chunk(ai, fc) < 0) panic("Failed to initialize percpu areas."); + pcpu_free_alloc_info(ai); } #endif /* CONFIG_SMP */
WARNING: multiple messages have this Message-ID (diff)
From: Nicolas Pitre <nicolas.pitre@linaro.org> To: Tejun Heo <tj@kernel.org> Cc: Christoph Lameter <cl@linux.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info Date: Tue, 3 Oct 2017 18:29:49 -0400 (EDT) [thread overview] Message-ID: <nycvar.YSQ.7.76.1710031731130.5407@knanqh.ubzr> (raw) In-Reply-To: <20171003210540.GM3301751@devbig577.frc2.facebook.com> On Tue, 3 Oct 2017, Tejun Heo wrote: > On Tue, Oct 03, 2017 at 04:57:44PM -0400, Nicolas Pitre wrote: > > This can be much smaller than a page on very small memory systems. > > Always rounding up the size to a page is wasteful in that case, and > > required alignment is smaller than the memblock default. Let's round > > things up to a page size only when the actual size is >= page size, and > > then it makes sense to page-align for a nicer allocation pattern. > > Isn't that a temporary area which gets freed later during boot? Hmmm... It may get freed through 3 different paths where 2 of them are error paths. What looks like a non-error path is in pcpu_embed_first_chunk() called from setup_per_cpu_areas(). But there are two versions of setup_per_cpu_areas(): one for SMP and one for !SMP. And the !SMP case never calls pcpu_free_alloc_info() currently. I'm not sure i understand that code fully, but maybe the following patch could be a better fit: ----- >8 Subject: [PATCH] percpu: don't forget to free the temporary struct pcpu_alloc_info Unlike the SMP case, the !SMP case does not free the memory for struct pcpu_alloc_info allocated in setup_per_cpu_areas(). And to give it a chance of being reused by the page allocator later, align it to a page boundary just like its size. Signed-off-by: Nicolas Pitre <nico@linaro.org> diff --git a/mm/percpu.c b/mm/percpu.c index 434844415d..caab63375b 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1416,7 +1416,7 @@ struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups, __alignof__(ai->groups[0].cpu_map[0])); ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]); - ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), 0); + ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), PAGE_SIZE); if (!ptr) return NULL; ai = ptr; @@ -2295,6 +2295,7 @@ void __init setup_per_cpu_areas(void) if (pcpu_setup_first_chunk(ai, fc) < 0) panic("Failed to initialize percpu areas."); + pcpu_free_alloc_info(ai); } #endif /* CONFIG_SMP */ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-10-03 22:29 UTC|newest] Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-03 20:57 [PATCH] mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info Nicolas Pitre 2017-10-03 20:57 ` Nicolas Pitre 2017-10-03 21:05 ` Tejun Heo 2017-10-03 21:05 ` Tejun Heo 2017-10-03 22:29 ` Nicolas Pitre [this message] 2017-10-03 22:29 ` Nicolas Pitre 2017-10-03 22:36 ` Tejun Heo 2017-10-03 22:36 ` Tejun Heo 2017-10-03 23:48 ` Dennis Zhou 2017-10-03 23:48 ` Dennis Zhou 2017-10-04 0:13 ` Nicolas Pitre 2017-10-04 0:13 ` Nicolas Pitre 2017-10-04 14:15 ` Tejun Heo 2017-10-04 14:15 ` Tejun Heo 2017-11-18 18:25 ` mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info (crisv32 hang) Guenter Roeck 2017-11-18 18:25 ` Guenter Roeck 2017-11-19 20:36 ` Nicolas Pitre 2017-11-19 20:36 ` Nicolas Pitre 2017-11-20 2:03 ` Guenter Roeck 2017-11-20 2:03 ` Guenter Roeck 2017-11-20 4:08 ` Nicolas Pitre 2017-11-20 4:08 ` Nicolas Pitre 2017-11-20 5:05 ` Guenter Roeck 2017-11-20 5:05 ` Guenter Roeck 2017-11-20 18:18 ` Nicolas Pitre 2017-11-20 18:18 ` Nicolas Pitre 2017-11-20 18:51 ` Guenter Roeck 2017-11-20 18:51 ` Guenter Roeck 2017-11-20 20:21 ` Nicolas Pitre 2017-11-20 20:21 ` Nicolas Pitre 2017-11-20 21:11 ` Guenter Roeck 2017-11-20 21:11 ` Guenter Roeck 2017-11-21 0:28 ` Nicolas Pitre 2017-11-21 0:28 ` Nicolas Pitre 2017-11-21 1:48 ` Guenter Roeck 2017-11-21 1:48 ` Guenter Roeck 2017-11-21 3:50 ` Nicolas Pitre 2017-11-21 3:50 ` Nicolas Pitre 2017-11-22 15:34 ` Jesper Nilsson 2017-11-22 15:34 ` Jesper Nilsson 2017-11-22 20:17 ` Nicolas Pitre 2017-11-22 20:17 ` Nicolas Pitre 2017-11-23 7:56 ` Jesper Nilsson 2017-11-23 7:56 ` Jesper Nilsson 2017-11-27 19:41 ` Tejun Heo 2017-11-27 19:41 ` Tejun Heo 2017-11-27 20:31 ` Nicolas Pitre 2017-11-27 20:31 ` Nicolas Pitre 2017-11-27 20:33 ` Tejun Heo 2017-11-27 20:33 ` Tejun Heo 2017-11-27 20:51 ` Nicolas Pitre 2017-11-27 20:51 ` Nicolas Pitre 2017-11-27 20:54 ` Tejun Heo 2017-11-27 20:54 ` Tejun Heo 2017-11-27 21:11 ` Guenter Roeck 2017-11-27 21:11 ` Guenter Roeck 2017-11-28 8:19 ` Jesper Nilsson 2017-11-28 8:19 ` Jesper Nilsson
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