On Thu, Sep 28, 2023 at 04:33:02PM +0800, Yajun Deng wrote: > memmap_init_range() would init page count of all pages, but the free > pages count would be reset in __free_pages_core(). There are opposite > operations. It's unnecessary and time-consuming when it's MEMINIT_EARLY > context. > > Init page count in reserve_bootmem_region when in MEMINIT_EARLY context, > and check the page count before reset it. > > At the same time, the INIT_LIST_HEAD in reserve_bootmem_region isn't > need, as it already done in __init_single_page. > > The following data was tested on an x86 machine with 190GB of RAM. > > before: > free_low_memory_core_early() 341ms > > after: > free_low_memory_core_early() 285ms > > Signed-off-by: Yajun Deng <yajun.deng@xxxxxxxxx> > --- > v4: same with v2. > v3: same with v2. > v2: check page count instead of check context before reset it. > v1: https://lore.kernel.org/all/20230922070923.355656-1-yajun.deng@xxxxxxxxx/ > --- > mm/mm_init.c | 18 +++++++++++++----- > mm/page_alloc.c | 20 ++++++++++++-------- > 2 files changed, 25 insertions(+), 13 deletions(-) > > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 9716c8a7ade9..3ab8861e1ef3 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -718,7 +718,7 @@ static void __meminit init_reserved_page(unsigned long pfn, int nid) > if (zone_spans_pfn(zone, pfn)) > break; > } > - __init_single_page(pfn_to_page(pfn), pfn, zid, nid, INIT_PAGE_COUNT); > + __init_single_page(pfn_to_page(pfn), pfn, zid, nid, 0); > } > #else > static inline void pgdat_set_deferred_range(pg_data_t *pgdat) {} > @@ -756,8 +756,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, > > init_reserved_page(start_pfn, nid); > > - /* Avoid false-positive PageTail() */ > - INIT_LIST_HEAD(&page->lru); > + /* Init page count for reserved region */ Please add a comment that describes _why_ we initialize the page count here. > + init_page_count(page); > > /* > * no need for atomic set_bit because the struct > @@ -888,9 +888,17 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone > } > > page = pfn_to_page(pfn); > - __init_single_page(page, pfn, zone, nid, INIT_PAGE_COUNT); > - if (context == MEMINIT_HOTPLUG) > + > + /* If the context is MEMINIT_EARLY, we will init page count and > + * mark page reserved in reserve_bootmem_region, the free region > + * wouldn't have page count and we will check the pages count > + * in __free_pages_core. > + */ > + __init_single_page(page, pfn, zone, nid, 0); > + if (context == MEMINIT_HOTPLUG) { > + init_page_count(page); > __SetPageReserved(page); Rather than calling init_page_count() and __SetPageReserved() for MEMINIT_HOTPLUG you can set flags to INIT_PAGE_COUNT | INIT_PAGE_RESERVED an call __init_single_page() after the check for MEMINIT_HOTPLUG. But more generally, I wonder if we have to differentiate HOTPLUG here at all. @David, can you comment please? > + } > > /* > * Usually, we want to mark the pageblock MIGRATE_MOVABLE, > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 06be8821d833..b868caabe8dc 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1285,18 +1285,22 @@ void __free_pages_core(struct page *page, unsigned int order) > unsigned int loop; > > /* > - * When initializing the memmap, __init_single_page() sets the refcount > - * of all pages to 1 ("allocated"/"not free"). We have to set the > - * refcount of all involved pages to 0. > + * When initializing the memmap, memmap_init_range sets the refcount > + * of all pages to 1 ("reserved" and "free") in hotplug context. We > + * have to set the refcount of all involved pages to 0. Otherwise, > + * we don't do it, as reserve_bootmem_region only set the refcount on > + * reserve region ("reserved") in early context. > */ Again, why hotplug and early init should be different? > - prefetchw(p); > - for (loop = 0; loop < (nr_pages - 1); loop++, p++) { > - prefetchw(p + 1); > + if (page_count(page)) { > + prefetchw(p); > + for (loop = 0; loop < (nr_pages - 1); loop++, p++) { > + prefetchw(p + 1); > + __ClearPageReserved(p); > + set_page_count(p, 0); > + } > __ClearPageReserved(p); > set_page_count(p, 0); > } > - __ClearPageReserved(p); > - set_page_count(p, 0); > > atomic_long_add(nr_pages, &page_zone(page)->managed_pages); > > -- > 2.25.1 > -- Sincerely yours, Mike.
