On 14/11/2024 11:15, Vlastimil Babka wrote: > On 10/14/24 12:58, Ryan Roberts wrote: >> To prepare for supporting boot-time page size selection, refactor code >> to remove assumptions about PAGE_SIZE being compile-time constant. Code >> intended to be equivalent when compile-time page size is active. >> >> "union handle_parts" previously calculated the number of bits required >> for its pool index and offset members based on PAGE_SHIFT. This is >> problematic for boot-time page size builds because the actual page size >> isn't known until boot-time. >> >> We could use PAGE_SHIFT_MAX in calculating the worst case offset bits, >> but bits would be wasted that could be used for pool index when >> PAGE_SIZE is set smaller than MAX, the end result being that stack depot >> can address less memory than it should. >> >> To avoid needing to dynamically define the offset and index bit widths, >> let's instead fix the pool size and derive the order at runtime based on >> the PAGE_SIZE. This means that the fields' widths can remain static, >> with the down side being slightly increased risk of failing to allocate >> the large folio. >> >> This only affects boot-time page size builds. compile-time page size >> builds will still always allocate order-2 folios. >> >> Additionally, wrap global variables that are initialized with PAGE_SIZE >> derived values using DEFINE_GLOBAL_PAGE_SIZE_VAR() so their >> initialization can be deferred for boot-time page size builds. > > This is done for pool_offset but given it's initialized by DEPOT_POOL_SIZE, > it doesn't look derived from PAGE_SIZE? Good spot; I think I initially did this when DEPOT_POOL_SIZE was still based on PAGE_SIZE. But then I've subsequently re-defined DEPOT_POOL_SIZE to be independent of PAGE_SIZE. I'll remove this part of the change. > >> >> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> > > Other than that, > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Thanks! > > >> --- >> >> ***NOTE*** >> Any confused maintainers may want to read the cover note here for context: >> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@xxxxxxx/ >> >> include/linux/stackdepot.h | 6 +++--- >> lib/stackdepot.c | 6 +++--- >> 2 files changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h >> index e9ec32fb97d4a..ac877a4e90406 100644 >> --- a/include/linux/stackdepot.h >> +++ b/include/linux/stackdepot.h >> @@ -32,10 +32,10 @@ typedef u32 depot_stack_handle_t; >> >> #define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8) >> >> -#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */ >> -#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER)) >> +#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages of PAGE_SIZE_MAX */ >> +#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT_MAX + DEPOT_POOL_ORDER)) >> #define DEPOT_STACK_ALIGN 4 >> -#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN) >> +#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT_MAX - DEPOT_STACK_ALIGN) >> #define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \ >> STACK_DEPOT_EXTRA_BITS) >> >> diff --git a/lib/stackdepot.c b/lib/stackdepot.c >> index 5ed34cc963fc3..974351f0e9e3c 100644 >> --- a/lib/stackdepot.c >> +++ b/lib/stackdepot.c >> @@ -68,7 +68,7 @@ static void *new_pool; >> /* Number of pools in stack_pools. */ >> static int pools_num; >> /* Offset to the unused space in the currently used pool. */ >> -static size_t pool_offset = DEPOT_POOL_SIZE; >> +static DEFINE_GLOBAL_PAGE_SIZE_VAR(size_t, pool_offset, DEPOT_POOL_SIZE); >> /* Freelist of stack records within stack_pools. */ >> static LIST_HEAD(free_stacks); >> /* The lock must be held when performing pool or freelist modifications. */ >> @@ -625,7 +625,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, >> */ >> if (unlikely(can_alloc && !READ_ONCE(new_pool))) { >> page = alloc_pages(gfp_nested_mask(alloc_flags), >> - DEPOT_POOL_ORDER); >> + get_order(DEPOT_POOL_SIZE)); >> if (page) >> prealloc = page_address(page); >> } >> @@ -663,7 +663,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, >> exit: >> if (prealloc) { >> /* Stack depot didn't use this memory, free it. */ >> - free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); >> + free_pages((unsigned long)prealloc, get_order(DEPOT_POOL_SIZE)); >> } >> if (found) >> handle = found->handle.handle; >
