On Wed, Dec 16, 2020 at 4:43 AM Vijayanand Jitta <vji...@codeaurora.org> wrote: > > > > 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 <vji...@codeaurora.org> > >> wrote: > >>> > >>> > >>> > >>> On 12/11/2020 6:55 PM, Alexander Potapenko wrote: > >>>> On Fri, Dec 11, 2020 at 1:45 PM Vijayanand Jitta <vji...@codeaurora.org> > >>>> wrote: > >>>>> > >>>>> > >>>>> > >>>>> On 12/11/2020 2:06 PM, Alexander Potapenko wrote: > >>>>>> On Thu, Dec 10, 2020 at 6:01 AM <vji...@codeaurora.org> wrote: > >>>>>>> > >>>>>>> From: Yogesh Lal <y...@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.
I still think there are implicit assumptions that should at least be written down in the comments. As far as I understand the code, here is what happens here: 0. No stacks are recorded. 1. early_param is called to set stack_hash_order to a value potentially smaller than MAX_STACK_HASH_SIZE. 2. KASAN (or other users) records some stacks into stack_table_def (capped at new STACK_HASH_SIZE) 3. init_stackdepot() allocates a new stack_table and copies the contents of stack_table_def into it 4. Further stacks are recorded into the new stack_table If this is how the things work, I agree we don't need to account for the part of stack_table_def past STACK_HASH_SIZE. Not allocating stack_table when setting stack_hash_order is probably also justified, as we don't have SLAB or vmalloc at that point. But I am still curious if a runtime parameter that disables the stackdepot completely will solve your problem. Allocating a small amount of memory when you actually don't want to allocate any sounds suboptimal. > 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 -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg