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? > > Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> Other than that, Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > --- > > ***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;
