From: Peng Fan <peng.fan@nxp.com>
To: Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux.com>
Cc: Vlad Buslov <vladbu@mellanox.com>,
"kernel-team@fb.com" <kernel-team@fb.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 02/12] percpu: do not search past bitmap when allocating an area
Date: Sat, 2 Mar 2019 13:32:04 +0000 [thread overview]
Message-ID: <AM0PR04MB4481E8B4E51EB7FCFA72ABF088770@AM0PR04MB4481.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20190228021839.55779-3-dennis@kernel.org>
Hi Dennis,
> -----Original Message-----
> From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On
> Behalf Of Dennis Zhou
> Sent: 2019年2月28日 10:18
> To: Dennis Zhou <dennis@kernel.org>; Tejun Heo <tj@kernel.org>; Christoph
> Lameter <cl@linux.com>
> Cc: Vlad Buslov <vladbu@mellanox.com>; kernel-team@fb.com;
> linux-mm@kvack.org; linux-kernel@vger.kernel.org
> Subject: [PATCH 02/12] percpu: do not search past bitmap when allocating an
> area
>
> pcpu_find_block_fit() guarantees that a fit is found within
> PCPU_BITMAP_BLOCK_BITS. Iteration is used to determine the first fit as it
> compares against the block's contig_hint. This can lead to incorrectly scanning
> past the end of the bitmap. The behavior was okay given the check after for
> bit_off >= end and the correctness of the hints from pcpu_find_block_fit().
>
> This patch fixes this by bounding the end offset by the number of bits in a
> chunk.
>
> Signed-off-by: Dennis Zhou <dennis@kernel.org>
> ---
> mm/percpu.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 53bd79a617b1..69ca51d238b5 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -988,7 +988,8 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk,
> int alloc_bits,
> /*
> * Search to find a fit.
> */
> - end = start + alloc_bits + PCPU_BITMAP_BLOCK_BITS;
> + end = min_t(int, start + alloc_bits + PCPU_BITMAP_BLOCK_BITS,
> + pcpu_chunk_map_bits(chunk));
> bit_off = bitmap_find_next_zero_area(chunk->alloc_map, end, start,
> alloc_bits, align_mask);
> if (bit_off >= end)
> --
From pcpu_alloc_area itself, I think this is correct to avoid bitmap_find_next_zero_area
scan past the boundaries of alloc_map, so
Reviewed-by: Peng Fan <peng.fan@nxp.com>
There are a few points I did not understand well,
Per understanding pcpu_find_block_fit is to find the first bit off in a chunk which could satisfy
the bits allocation, so bits might be larger than PCPU_BITMAP_BLOCK_BITS. And if
pcpu_find_block_fit returns a good off, it means there is a area in the chunk could satisfy
the bits allocation, then the following pcpu_alloc_area will not scan past the boundaries of
alloc_map, right?
Thanks,
Peng.
> 2.17.1
next prev parent reply other threads:[~2019-03-02 13:32 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-28 2:18 [PATCH 00/12] introduce percpu block scan_hint Dennis Zhou
2019-02-28 2:18 ` [PATCH 01/12] percpu: update free path with correct new free region Dennis Zhou
2019-03-02 12:56 ` Peng Fan
2019-02-28 2:18 ` [PATCH 02/12] percpu: do not search past bitmap when allocating an area Dennis Zhou
2019-03-02 13:32 ` Peng Fan [this message]
2019-03-02 22:23 ` Dennis Zhou
2019-03-03 8:41 ` Peng Fan
2019-02-28 2:18 ` [PATCH 03/12] percpu: introduce helper to determine if two regions overlap Dennis Zhou
2019-03-02 13:37 ` Peng Fan
2019-03-02 22:24 ` Dennis Zhou
2019-02-28 2:18 ` [PATCH 04/12] percpu: manage chunks based on contig_bits instead of free_bytes Dennis Zhou
2019-03-02 13:48 ` Peng Fan
2019-03-02 22:32 ` Dennis Zhou
2019-03-03 8:42 ` Peng Fan
2019-02-28 2:18 ` [PATCH 05/12] percpu: relegate chunks unusable when failing small allocations Dennis Zhou
2019-03-02 13:55 ` Peng Fan
2019-03-02 22:34 ` Dennis Zhou
2019-02-28 2:18 ` [PATCH 06/12] percpu: set PCPU_BITMAP_BLOCK_SIZE to PAGE_SIZE Dennis Zhou
2019-03-03 4:56 ` Peng Fan
2019-02-28 2:18 ` [PATCH 07/12] percpu: add block level scan_hint Dennis Zhou
2019-03-03 6:01 ` Peng Fan
2019-03-03 20:23 ` Dennis Zhou
2019-03-04 9:36 ` Peng Fan
2019-02-28 2:18 ` [PATCH 08/12] percpu: remember largest area skipped during allocation Dennis Zhou
2019-02-28 2:18 ` [PATCH 09/12] percpu: use block scan_hint to only scan forward Dennis Zhou
2019-02-28 2:18 ` [PATCH 10/12] percpu: make pcpu_block_md generic Dennis Zhou
2019-03-03 6:35 ` Peng Fan
2019-02-28 2:18 ` [PATCH 11/12] percpu: convert chunk hints to be based on pcpu_block_md Dennis Zhou
2019-03-03 8:18 ` Peng Fan
2019-03-03 20:22 ` Dennis Zhou
2019-03-04 6:36 ` Peng Fan
2019-02-28 2:18 ` [PATCH 12/12] percpu: use chunk scan_hint to skip some scanning Dennis Zhou
2019-03-03 8:38 ` Peng Fan
2019-02-28 14:47 ` [PATCH 00/12] introduce percpu block scan_hint Vlad Buslov
2019-03-13 20:19 ` Dennis Zhou
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