Messages in this thread |  | | Subject | Re: [PATCH v3] lib: stackdepot: Add support to configure STACK_HASH_SIZE | | From | Vijayanand Jitta <> | | Date | Mon, 14 Dec 2020 09:32:33 +0530 |
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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
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
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