The patch titled Subject: mm: page_alloc: skip regions with hugetlbfs pages when allocating 1G pages has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-page_alloc-skip-regions-with-hugetlbfs-pages-when-allocating-1g-pages.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Mel Gorman mgorman@techsingularity.net Subject: mm: page_alloc: skip regions with hugetlbfs pages when allocating 1G pages Date: Fri, 14 Apr 2023 15:14:29 +0100

A bug was reported by Yuanxi Liu where allocating 1G pages at runtime is taking an excessive amount of time for large amounts of memory. Further testing allocating huge pages that the cost is linear i.e. if allocating 1G pages in batches of 10 then the time to allocate nr_hugepages from 10->20->30->etc increases linearly even though 10 pages are allocated at each step. Profiles indicated that much of the time is spent checking the validity within already existing huge pages and then attempting a migration that fails after isolating the range, draining pages and a whole lot of other useless work.

Commit eb14d4eefdc4 ("mm,page_alloc: drop unnecessary checks from pfn_range_valid_contig") removed two checks, one which ignored huge pages for contiguous allocations as huge pages can sometimes migrate. While there may be value on migrating a 2M page to satisfy a 1G allocation, it's potentially expensive if the 1G allocation fails and it's pointless to try moving a 1G page for a new 1G allocation or scan the tail pages for valid PFNs.

Reintroduce the PageHuge check and assume any contiguous region with hugetlbfs pages is unsuitable for a new 1G allocation.

The hpagealloc test allocates huge pages in batches and reports the average latency per page over time. This test happens just after boot when fragmentation is not an issue. Units are in milliseconds.

hpagealloc 6.3.0-rc6 6.3.0-rc6 6.3.0-rc6 vanilla hugeallocrevert-v1r1 hugeallocsimple-v1r2 Min Latency 26.42 ( 0.00%) 5.07 ( 80.82%) 18.94 ( 28.30%) 1st-qrtle Latency 356.61 ( 0.00%) 5.34 ( 98.50%) 19.85 ( 94.43%) 2nd-qrtle Latency 697.26 ( 0.00%) 5.47 ( 99.22%) 20.44 ( 97.07%) 3rd-qrtle Latency 972.94 ( 0.00%) 5.50 ( 99.43%) 20.81 ( 97.86%) Max-1 Latency 26.42 ( 0.00%) 5.07 ( 80.82%) 18.94 ( 28.30%) Max-5 Latency 82.14 ( 0.00%) 5.11 ( 93.78%) 19.31 ( 76.49%) Max-10 Latency 150.54 ( 0.00%) 5.20 ( 96.55%) 19.43 ( 87.09%) Max-90 Latency 1164.45 ( 0.00%) 5.53 ( 99.52%) 20.97 ( 98.20%) Max-95 Latency 1223.06 ( 0.00%) 5.55 ( 99.55%) 21.06 ( 98.28%) Max-99 Latency 1278.67 ( 0.00%) 5.57 ( 99.56%) 22.56 ( 98.24%) Max Latency 1310.90 ( 0.00%) 8.06 ( 99.39%) 26.62 ( 97.97%) Amean Latency 678.36 ( 0.00%) 5.44 * 99.20%* 20.44 * 96.99%*

6.3.0-rc6 6.3.0-rc6 6.3.0-rc6 vanilla revert-v1 hugeallocfix-v2 Duration User 0.28 0.27 0.30 Duration System 808.66 17.77 35.99 Duration Elapsed 830.87 18.08 36.33

The vanilla kernel is poor, taking up to 1.3 second to allocate a huge page and almost 10 minutes in total to run the test. Reverting the problematic commit reduces it to 8ms at worst and the patch takes 26ms. This patch fixes the main issue with skipping huge pages but leaves the page_count() out because a page with an elevated count potentially can migrate.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=217022 Link: https://lkml.kernel.org/r/20230414141429.pwgieuwluxwez3rj@techsingularity.ne... Fixes: eb14d4eefdc4 ("mm,page_alloc: drop unnecessary checks from pfn_range_valid_contig") Signed-off-by: Mel Gorman mgorman@techsingularity.net Reported-by: Yuanxi Liu y.liu@naruida.com Acked-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: David Hildenbrand david@redhat.com Acked-by: Michal Hocko mhocko@suse.com Cc: Matthew Wilcox willy@infradead.org Cc: Oscar Salvador OSalvador@suse.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_alloc.c | 3 +++ 1 file changed, 3 insertions(+)

--- a/mm/page_alloc.c~mm-page_alloc-skip-regions-with-hugetlbfs-pages-when-allocating-1g-pages +++ a/mm/page_alloc.c @@ -9466,6 +9466,9 @@ static bool pfn_range_valid_contig(struc

if (PageReserved(page)) return false; + + if (PageHuge(page)) + return false; } return true; } _

Patches currently in -mm which might be from mgorman@techsingularity.net are

mm-page_alloc-skip-regions-with-hugetlbfs-pages-when-allocating-1g-pages.patch