Commit 7f24cbc9 authored Oct 07, 2024 by Oscar Salvador Committed by Andrew Morton Nov 06, 2024

mm/mmap: teach generic_get_unmapped_area{_topdown} to handle hugetlb mappings

Patch series "Unify hugetlb into arch_get_unmapped_area functions", v4.

This is an attempt to get rid of a fair amount of duplicated code wrt. 
hugetlb and *get_unmapped_area* functions.

HugeTLB registers a .get_unmapped_area function which gets called from
__get_unmapped_area().
hugetlb_get_unmapped_area() is defined by a bunch of architectures and
it also has a generic definition for those that do not define it.
Short-long story is that there is a ton of duplicated code between
specific hugetlb *_get_unmapped_area_* functions and mm-core functions,
so we can do better by teaching arch_get_unmapped_area* functions how
to deal with hugetlb mappings.

Note that not a lot of things need to be taught though. 
hugetlb_get_unmapped_area, that gets called for hugetlb mappings, runs
some sanity checks prior to calling mm_get_unmapped_area_vmflags(), so we
do not need to that down the road in the respective
{generic,arch}_get_unmapped_area* functions.

More information can be found in the respective patches.

LTP mmapstress hugetlb selftests were ran succesfully on:


This patch (of 9):

We want to stop special casing hugetlb mappings and make them go through
generic channels, so teach generic_get_unmapped_area{_topdown} to handle
those.  The main difference is that we set info.align_mask for huge
mappings.

Link: https://lkml.kernel.org/r/20241007075037.267650-1-osalvador@suse.de
Link: https://lkml.kernel.org/r/20241007075037.267650-2-osalvador@suse.de


Signed-off-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 04f315a7

include/linux/hugetlb.h

+10 −0

Original line number	Diff line number	Diff line
		@@ -1035,9 +1035,19 @@ void hugetlb_unregister_node(struct node *node);
		*/
		bool is_raw_hwpoison_page_in_hugepage(struct page *page);

		static inline unsigned long huge_page_mask_align(struct file *file)
		{
		return PAGE_MASK & ~huge_page_mask(hstate_file(file));
		}

		#else /* CONFIG_HUGETLB_PAGE */
		struct hstate {};

		static inline unsigned long huge_page_mask_align(struct file *file)
		{
		return 0;
		}

		static inline struct hugepage_subpool hugetlb_folio_subpool(struct folio folio)
		{
		return NULL;

mm/mmap.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -776,6 +776,8 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
		info.low_limit = mm->mmap_base;
		info.high_limit = mmap_end;
		info.start_gap = stack_guard_placement(vm_flags);
		if (filp && is_file_hugepages(filp))
		info.align_mask = huge_page_mask_align(filp);
		return vm_unmapped_area(&info);
		}

		@@ -826,6 +828,8 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
		info.low_limit = PAGE_SIZE;
		info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
		info.start_gap = stack_guard_placement(vm_flags);
		if (filp && is_file_hugepages(filp))
		info.align_mask = huge_page_mask_align(filp);
		addr = vm_unmapped_area(&info);

		/*