> I dont like it either :) > Pressed "Ctrl+enter" instead of "enter" by mistake which sent the email prematurely :) Adding replies to the rest of the comments in this email. As I mentioned in reply to David now in [1], pageblock_nr_pages is not really 1 << PAGE_BLOCK_ORDER but is 1 << min(HPAGE_PMD_ORDER, PAGE_BLOCK_ORDER) when THP is enabled. It needs a better name, but I think the right approach is just to change pageblock_order as recommended in [2] [1] https://lore.kernel.org/all/4adf1f8b-781d-4ab0-b82e-49795ad712cb@xxxxxxxxx/ [2] https://lore.kernel.org/all/c600a6c0-aa59-4896-9e0d-3649a32d1771@xxxxxxxxx/ > >>> +{ >>> + return (1UL << min(thp_highest_allowable_order(), PAGE_BLOCK_ORDER)); >>> +} >>> + >>> static void set_recommended_min_free_kbytes(void) >>> { >>> struct zone *zone; >>> @@ -2638,12 +2658,16 @@ static void set_recommended_min_free_kbytes(void) >> >> You provide a 'patchlet' in >> https://lore.kernel.org/all/a179fd65-dc3f-4769-9916-3033497188ba@xxxxxxxxx/ >> >> That also does: >> >> /* Ensure 2 pageblocks are free to assist fragmentation avoidance */ >> - recommended_min = pageblock_nr_pages * nr_zones * 2; >> + recommended_min = min_thp_pageblock_nr_pages() * nr_zones * 2; >> >> So comment here - this comment is now incorrect, this isn't 2 page blocks, >> it's 2 of 'sub-pageblock size as if page blocks were dynamically altered by >> always/madvise THP size'. >> >> Again, this whole thing strikes me as we're doing things at the wrong level >> of abstraction. >> >> And you're definitely now not helping avoid pageblock-sized >> fragmentation. You're accepting that you need less so... why not reduce >> pageblock size? :) >> Yes agreed. >> /* >> * Make sure that on average at least two pageblocks are almost free >> * of another type, one for a migratetype to fall back to and a >> >> ^ remainder of comment >> >>> * second to avoid subsequent fallbacks of other types There are 3 >>> * MIGRATE_TYPES we care about. >>> */ >>> - recommended_min += pageblock_nr_pages * nr_zones * >>> + recommended_min += min_thp_pageblock_nr_pages() * nr_zones * >>> MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; >> >> This just seems wrong now and contradicts the comment - you're setting >> minimum pages based on migrate PCP types that operate at pageblock order >> but without reference to the actual number of page block pages? >> >> So the comment is just wrong now? 'make sure there are at least two >> pageblocks', well this isn't what you're doing is it? So why there are we >> making reference to PCP counts etc.? >> >> This seems like we're essentially just tuning these numbers someswhat >> arbitrarily to reduce them? >> >>> >>> - /* don't ever allow to reserve more than 5% of the lowmem */ >>> - recommended_min = min(recommended_min, >>> - (unsigned long) nr_free_buffer_pages() / 20); >>> + /* >>> + * Don't ever allow to reserve more than 5% of the lowmem. >>> + * Use a min of 128 pages when all THP orders are set to never. >> >> Why? Did you just choose this number out of the blue? Mentioned this in the previous comment. >> >> Previously, on x86-64 with thp -> never on everything a pageblock order-9 >> wouldn't this be a much higher value? >> >> I mean just putting '128' here is not acceptable. It needs to be justified >> (even if empirically with data to back it) and defined as a named thing. >> >> >>> + */ >>> + recommended_min = clamp(recommended_min, 128, >>> + (unsigned long) nr_free_buffer_pages() / 20); >>> + >>> recommended_min <<= (PAGE_SHIFT-10); >>> >>> if (recommended_min > min_free_kbytes) { >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 0c5fb4ffa03a..8e92678d1175 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -136,10 +136,10 @@ struct shmem_options { >>> }; >>> >>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> -static unsigned long huge_shmem_orders_always __read_mostly; >>> -static unsigned long huge_shmem_orders_madvise __read_mostly; >>> -static unsigned long huge_shmem_orders_inherit __read_mostly; >>> -static unsigned long huge_shmem_orders_within_size __read_mostly; >>> +unsigned long huge_shmem_orders_always __read_mostly; >>> +unsigned long huge_shmem_orders_madvise __read_mostly; >>> +unsigned long huge_shmem_orders_inherit __read_mostly; >>> +unsigned long huge_shmem_orders_within_size __read_mostly; >> >> Again, we really shouldn't need to do this. Agreed, for the RFC, I just did it similar to the anon ones when I got the build error trying to use these, but yeah a much better approach would be to just have a function in shmem that would return the largest shmem thp allowable order. >> >>> static bool shmem_orders_configured __initdata; >>> #endif >>> >>> @@ -516,25 +516,6 @@ static bool shmem_confirm_swap(struct address_space *mapping, >>> return xa_load(&mapping->i_pages, index) == swp_to_radix_entry(swap); >>> } >>> >>> -/* >>> - * Definitions for "huge tmpfs": tmpfs mounted with the huge= option >>> - * >>> - * SHMEM_HUGE_NEVER: >>> - * disables huge pages for the mount; >>> - * SHMEM_HUGE_ALWAYS: >>> - * enables huge pages for the mount; >>> - * SHMEM_HUGE_WITHIN_SIZE: >>> - * only allocate huge pages if the page will be fully within i_size, >>> - * also respect madvise() hints; >>> - * SHMEM_HUGE_ADVISE: >>> - * only allocate huge pages if requested with madvise(); >>> - */ >>> - >>> -#define SHMEM_HUGE_NEVER 0 >>> -#define SHMEM_HUGE_ALWAYS 1 >>> -#define SHMEM_HUGE_WITHIN_SIZE 2 >>> -#define SHMEM_HUGE_ADVISE 3 >>> - >> >> Again we really shouldn't need to do this, just provide some function from >> shmem that gives you what you need. >> >>> /* >>> * Special values. >>> * Only can be set via /sys/kernel/mm/transparent_hugepage/shmem_enabled: >>> @@ -551,7 +532,7 @@ static bool shmem_confirm_swap(struct address_space *mapping, >>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> /* ifdef here to avoid bloating shmem.o when not necessary */ >>> >>> -static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER; >>> +int shmem_huge __read_mostly = SHMEM_HUGE_NEVER; >> >> Same comment. >> >>> static int tmpfs_huge __read_mostly = SHMEM_HUGE_NEVER; >>> >>> /** >>> -- >>> 2.47.1 >>> >
