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Subject: Re: [PATCH] lib: stackdepot: Add support to configure STACK_HASH_SIZE
To:     Minchan Kim <minchan@kernel.org>, linux-mm <linux-mm@kvack.org>
Cc:     glider@google.com, Dan Williams <dan.j.williams@intel.com>,
        broonie@kernel.org, mhiramat@kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yogesh Lal <ylal@codeaurora.org>,
        Vinayak Menon <vinmenon@codeaurora.org>
References: <1603372546-27118-1-git-send-email-vjitta@codeaurora.org>
 <CAEwNFnBvxu7+oNkcO9D70OFrxQXswcJG4OvDPyzNf7kpXfpSuw@mail.gmail.com>
From:   Vijayanand Jitta <vjitta@codeaurora.org>
Message-ID: <282d7028-498d-50b3-37d4-2381571f9f9e@codeaurora.org>
Date:   Wed, 4 Nov 2020 15:59:16 +0530
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On 11/4/2020 4:57 AM, Minchan Kim wrote:
> Sorry if this mail corrupts the mail thread or had heavy mangling
> since I lost this mail from my mailbox so I am sending this mail by
> web gmail.
> 
> On Thu, Oct 22, 2020 at 10:18 AM <vjitta@codeaurora.org> wrote:
>>
>> From: Yogesh Lal <ylal@codeaurora.org>
>>
>> Use STACK_HASH_ORDER_SHIFT to configure STACK_HASH_SIZE.
>>
>> Aim is to have configurable value for  STACK_HASH_SIZE,
>> so depend on use case one can configure it.
>>
>> One example is of Page Owner, default value of
>> STACK_HASH_SIZE lead stack depot to consume 8MB of static memory.
>> Making it configurable and use lower value helps to enable features like
>> CONFIG_PAGE_OWNER without any significant overhead.
>>
>> Signed-off-by: Yogesh Lal <ylal@codeaurora.org>
>> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
>> Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
>> ---
>>  lib/Kconfig      | 9 +++++++++
>>  lib/stackdepot.c | 3 +--
>>  2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/Kconfig b/lib/Kconfig
>> index 18d76b6..b3f8259 100644
>> --- a/lib/Kconfig
>> +++ b/lib/Kconfig
>> @@ -651,6 +651,15 @@ config STACKDEPOT
>>         bool
>>         select STACKTRACE
>>
>> +config STACK_HASH_ORDER_SHIFT
>> +       int "stack depot hash size (12 => 4KB, 20 => 1024KB)"
>> +       range 12 20
>> +       default 20
>> +       depends on STACKDEPOT
>> +       help
>> +        Select the hash size as a power of 2 for the stackdepot hash table.
>> +        Choose a lower value to reduce the memory impact.
>> +
>>  config SBITMAP
>>         bool
>>
>> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
>> index 2caffc6..413c20b 100644
>> --- a/lib/stackdepot.c
>> +++ b/lib/stackdepot.c
>> @@ -142,8 +142,7 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
>>         return stack;
>>  }
>>
>> -#define STACK_HASH_ORDER 20
>> -#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
>> +#define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER_SHIFT)
>>  #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
>>  #define STACK_HASH_SEED 0x9747b28c
>>
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
>> 2.7.4
>>
> 
> 1. When we don't use page_owner, we don't want to waste any memory for
> stackdepot hash array.
> 2. When we use page_owner, we want to have reasonable stackdeport hash array
> 
> With this configuration, it couldn't meet since we always need to
> reserve a reasonable size for the array.
> Can't we make the hash size as a kernel parameter?
> With it, we could use it like this.
> 
> 1. page_owner=off, stackdepot_stack_hash=0 -> no more wasted memory
> when we don't use page_owner
> 2. page_owner=on, stackdepot_stack_hash=8M -> reasonable hash size
> when we use page_owner.
> 
> 

This idea looks fine to me. Andrew and others would like to hear your
comments as well on this before implementing.

Thanks,
Vijay
-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of Code Aurora Forum, hosted by The Linux Foundation