From 5b24eeef06701cca6852f1bf768248ccc912819b Mon Sep 17 00:00:00 2001 From: Joao Martins Date: Fri, 14 Jan 2022 14:04:15 -0800 Subject: [PATCH] mm/page_alloc: split prep_compound_page into head and tail subparts Patch series "mm, device-dax: Introduce compound pages in devmap", v7. This series converts device-dax to use compound pages, and moves away from the 'struct page per basepage on PMD/PUD' that is done today. Doing so 1) unlocks a few noticeable improvements on unpin_user_pages() and makes device-dax+altmap case 4x times faster in pinning (numbers below and in last patch) 2) as mentioned in various other threads it's one important step towards cleaning up ZONE_DEVICE refcounting. I've split the compound pages on devmap part from the rest based on recent discussions on devmap pending and future work planned[5][6]. There is consensus that device-dax should be using compound pages to represent its PMD/PUDs just like HugeTLB and THP, and that leads to less specialization of the dax parts. I will pursue the rest of the work in parallel once this part is merged, particular the GUP-{slow,fast} improvements [7] and the tail struct page deduplication memory savings part[8]. To summarize what the series does: Patch 1: Prepare hwpoisoning to work with dax compound pages. Patches 2-3: Split the current utility function of prep_compound_page() into head and tail and use those two helpers where appropriate to take advantage of caches being warm after __init_single_page(). This is used when initializing zone device when we bring up device-dax namespaces. Patches 4-10: Add devmap support for compound pages in device-dax. memmap_init_zone_device() initialize its metadata as compound pages, and it introduces a new devmap property known as vmemmap_shift which outlines how the vmemmap is structured (defaults to base pages as done today). The property describe the page order of the metadata essentially. While at it do a few cleanups in device-dax in patches 5-9. Finally enable device-dax usage of devmap @vmemmap_shift to a value based on its own @align property. @vmemmap_shift returns 0 by default (which is today's case of base pages in devmap, like fsdax or the others) and the usage of compound devmap is optional. Starting with device-dax (*not* fsdax) we enable it by default. There are a few pinning improvements particular on the unpinning case and altmap, as well as unpin_user_page_range_dirty_lock() being just as effective as THP/hugetlb[0] pages. $ gup_test -f /dev/dax1.0 -m 16384 -r 10 -S -a -n 512 -w (pin_user_pages_fast 2M pages) put:~71 ms -> put:~22 ms [altmap] (pin_user_pages_fast 2M pages) get:~524ms put:~525 ms -> get: ~127ms put:~71ms $ gup_test -f /dev/dax1.0 -m 129022 -r 10 -S -a -n 512 -w (pin_user_pages_fast 2M pages) put:~513 ms -> put:~188 ms [altmap with -m 127004] (pin_user_pages_fast 2M pages) get:~4.1 secs put:~4.12 secs -> get:~1sec put:~563ms Tested on x86 with 1Tb+ of pmem (alongside registering it with RDMA with and without altmap), alongside gup_test selftests with dynamic dax regions and static dax regions. Coupled with ndctl unit tests for dynamic dax devices that exercise all of this. Note, for dynamic dax regions I had to revert commit 8aa83e6395 ("x86/setup: Call early_reserve_memory() earlier"), it is a known issue that this commit broke efi_fake_mem=. This patch (of 11): Split the utility function prep_compound_page() into head and tail counterparts, and use them accordingly. This is in preparation for sharing the storage for compound page metadata. Link: https://lkml.kernel.org/r/20211202204422.26777-1-joao.m.martins@oracle.com Link: https://lkml.kernel.org/r/20211202204422.26777-3-joao.m.martins@oracle.com Signed-off-by: Joao Martins Acked-by: Mike Kravetz Reviewed-by: Dan Williams Reviewed-by: Muchun Song Cc: Vishal Verma Cc: Dave Jiang Cc: Naoya Horiguchi Cc: Matthew Wilcox (Oracle) Cc: Jason Gunthorpe Cc: John Hubbard Cc: Jane Chu Cc: Jonathan Corbet Cc: Christoph Hellwig Cc: Jason Gunthorpe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index c595274..20b9db0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -726,23 +726,33 @@ void free_compound_page(struct page *page) free_the_page(page, compound_order(page)); } +static void prep_compound_head(struct page *page, unsigned int order) +{ + set_compound_page_dtor(page, COMPOUND_PAGE_DTOR); + set_compound_order(page, order); + atomic_set(compound_mapcount_ptr(page), -1); + if (hpage_pincount_available(page)) + atomic_set(compound_pincount_ptr(page), 0); +} + +static void prep_compound_tail(struct page *head, int tail_idx) +{ + struct page *p = head + tail_idx; + + p->mapping = TAIL_MAPPING; + set_compound_head(p, head); +} + void prep_compound_page(struct page *page, unsigned int order) { int i; int nr_pages = 1 << order; __SetPageHead(page); - for (i = 1; i < nr_pages; i++) { - struct page *p = page + i; - p->mapping = TAIL_MAPPING; - set_compound_head(p, page); - } + for (i = 1; i < nr_pages; i++) + prep_compound_tail(page, i); - set_compound_page_dtor(page, COMPOUND_PAGE_DTOR); - set_compound_order(page, order); - atomic_set(compound_mapcount_ptr(page), -1); - if (hpage_pincount_available(page)) - atomic_set(compound_pincount_ptr(page), 0); + prep_compound_head(page, order); } #ifdef CONFIG_DEBUG_PAGEALLOC -- 2.7.4