Messages in this thread | | | Subject | Re: [PATCH v3] lib: stackdepot: Add support to configure STACK_HASH_SIZE | From | Vijayanand Jitta <> | Date | Wed, 16 Dec 2020 09:13:28 +0530 |
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On 12/14/2020 4:02 PM, Vijayanand Jitta wrote: > > > On 12/14/2020 3:04 PM, Alexander Potapenko wrote: >> On Mon, Dec 14, 2020 at 5:02 AM Vijayanand Jitta <vjitta@codeaurora.org> wrote: >>> >>> >>> >>> On 12/11/2020 6:55 PM, Alexander Potapenko wrote: >>>> On Fri, Dec 11, 2020 at 1:45 PM Vijayanand Jitta <vjitta@codeaurora.org> wrote: >>>>> >>>>> >>>>> >>>>> On 12/11/2020 2:06 PM, Alexander Potapenko wrote: >>>>>> On Thu, Dec 10, 2020 at 6:01 AM <vjitta@codeaurora.org> wrote: >>>>>>> >>>>>>> From: Yogesh Lal <ylal@codeaurora.org> >>>>>>> >>>>>>> Add a kernel parameter stack_hash_order to configure STACK_HASH_SIZE. >>>>>>> >>>>>>> Aim is to have configurable value for STACK_HASH_SIZE, so that one >>>>>>> can configure it depending on usecase there by reducing the static >>>>>>> memory overhead. >>>>>>> >>>>>>> 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. >>>>>> >>>>>> Can we go with a static CONFIG_ parameter instead? >>>>>> Guess most users won't bother changing the default anyway, and for >>>>>> CONFIG_PAGE_OWNER users changing the size at boot time is not strictly >>>>>> needed. >>>>>> >>>>> Thanks for review. >>>>> >>>>> One advantage of having run time parameter is we can simply set it to a >>>>> lower value at runtime if page_owner=off thereby reducing the memory >>>>> usage or use default value if we want to use page owner so, we have some >>>>> some flexibility here. This is not possible with static parameter as we >>>>> have to have some predefined value. >>>> >>>> If we are talking about a configuration in which page_owner is the >>>> only stackdepot user in the system, then for page_owner=off it >>>> probably makes more sense to disable stackdepot completely instead of >>>> setting it to a lower value. This is a lot easier to do in terms of >>>> correctness. >>>> But if there are other users (e.g. KASAN), their stackdepot usage may >>>> actually dominate that of page_owner. >>>> >>>>>>> -static struct stack_record *stack_table[STACK_HASH_SIZE] = { >>>>>>> - [0 ... STACK_HASH_SIZE - 1] = NULL >>>>>>> +static unsigned int stack_hash_order = 20; >>>>>> >>>>>> Please initialize with MAX_STACK_HASH_ORDER instead. >>>>>> >>>>> >>>>> Sure, will update this. >>>>> >>>> >>>> >>>>>>> + >>>>>>> +static int __init init_stackdepot(void) >>>>>>> +{ >>>>>>> + size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *)); >>>>>>> + >>>>>>> + stack_table = vmalloc(size); >>>>>>> + memcpy(stack_table, stack_table_def, size); >>>>>> >>>>>> Looks like you are assuming stack_table_def already contains some data >>>>>> by this point. >>>>>> But if STACK_HASH_SIZE shrinks this memcpy() above will just copy some >>>>>> part of the table, whereas the rest will be lost. >>>>>> We'll need to: >>>>>> - either explicitly decide we can afford losing this data (no idea how >>>>>> bad this can potentially be), >>>>>> - or disallow storing anything prior to full stackdepot initialization >>>>>> (then we don't need stack_table_def), >>>>>> - or carefully move all entries to the first part of the table. >>>>>> >>>>>> Alex >>>>>> >>>>> >>>>> The hash for stack_table_def is computed using the run time parameter >>>>> stack_hash_order, though stack_table_def is a bigger array it will only >>>>> use the entries that are with in the run time configured STACK_HASH_SIZE >>>>> range. so, there will be no data loss during copy. >>>> >>>> Do we expect any data to be stored into stack_table_def before >>>> setup_stack_hash_order() is called? >>>> If the answer is no, then we could probably drop stack_table_def and >>>> allocate the table right in setup_stack_hash_order()? >>>> >>> >>> Yes, we do see an allocation from stack depot even before init is called >>> from kasan, thats the reason for having stack_table_def. >>> This is the issue reported due to that on v2, so i added stack_table_def. >>> https://lkml.org/lkml/2020/12/3/839 >> >> But at that point STACK_HASH_SIZE is still equal to 1L << >> MAX_STACK_HASH_ORDER, isn't it? >> Then we still need to take care of the records that fit into the >> bigger array, but not the smaller one. >> > > At this point early_param is already called which sets stack_hash_order. > So, STACK_HASH_SIZE will be set to this updated value and not > MAX_STACK_HASH_SIZE.So, no additional entires in the bigger array. > > Thanks, > Vijay >
Let me know if there are any other concerns.
Thanks, Vijay
>>> Thanks, >>> Vijay >>> >>>>> Thanks, >>>>> Vijay >>>>> >>>>> -- >>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a >>>>> member of Code Aurora Forum, hosted by The Linux Foundation >>>> >>>> >>>> >>> >>> -- >>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a >>> member of Code Aurora Forum, hosted by The Linux Foundation >> >> >> >
-- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
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