On Fri, Sep 29, 2023 at 06:27:25PM +0800, Yajun Deng wrote: > > On 2023/9/29 18:02, Mike Rapoport wrote: > > On Fri, Sep 29, 2023 at 05:50:40PM +0800, Yajun Deng wrote: > > > On 2023/9/29 16:30, Mike Rapoport wrote: > > > > 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. > > > Okay. > > > > > + 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. > > > No, the following code would cost more time than the current code in > > > memmap_init(). > > > > > > if (context == MEMINIT_HOTPLUG) > > > > > > __init_single_page(page, pfn, zone, nid, INIT_PAGE_COUNT | INIT_PAGE_RESERVED); > > > else > > > > > > __init_single_page(page, pfn, zone, nid, 0); > > Sorry if I wasn't clear. What I meant was to have something along these lines: > > > > enum page_init_flags flags = 0; > > > > if (context == MEMINIT_HOTPLUG) > > flags = INIT_PAGE_COUNT | INIT_PAGE_RESERVED; > > __init_single_page(page, pfn, zone, nid, flags); > > > Okay, I'll test the time consumed in memmap_init(). > > > > 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? > > > I will add a comment that describes it will save boot time. > > But why do we need initialize struct pages differently at boot time vs > > memory hotplug? > > Is there a reason memory hotplug cannot have page count set to 0 just like > > for pages reserved at boot time? > > This patch just save boot time in MEMINIT_EARLY. If someone finds out that > it can save time in > > MEMINIT_HOTPLUG, I think it can be done in another patch later. I just > keeping it in the same. But it's not the same. It becomes slower after your patch and the code that frees the pages for MEMINIT_EARLY and MEMINIT_HOTPLUG becomes non-uniform for no apparent reason. The if (page_count(page)) is really non-obvious... > > > > > - 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.
