Messages in this thread | | | Date | Fri, 29 Sep 2023 18:27:25 +0800 | Subject | Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when MEMINIT_EARLY | From | Yajun Deng <> |
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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@linux.dev> >>>> --- >>>> 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@linux.dev/ >>>> --- >>>> 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.
>>>> - 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 >>>>
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