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. > 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 -- 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