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This is an attempt to mitigate the issue of running out of memory when THP is always enabled. During runtime whenever a THP is being faulted in (__do_huge_pmd_anonymous_page) or collapsed by khugepaged (collapse_huge_page), the THP is added to _deferred_list. Whenever memory reclaim happens in linux, the kernel runs the deferred_split shrinker which goes through the _deferred_list. If the folio was partially mapped, the shrinker attempts to split it. If the folio is not partially mapped, the shrinker checks if the THP was underused, i.e. how many of the base 4K pages of the entire THP were zero-filled. If this number goes above a certain threshold (decided by /sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none), the shrinker will attempt to split that THP. Then at remap time, the pages that were zero-filled are mapped to the shared zeropage, hence saving memory. Link: https://lkml.kernel.org/r/20240830100438.3623486-6-usamaarif642@gmail.com Signed-off-by: Usama Arif <usamaarif642@gmail.com> Suggested-by: Rik van Riel <riel@surriel.com> Co-authored-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Alexander Zhu <alexlzhu@fb.com> Cc: Barry Song <baohua@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Kairui Song <ryncsn@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mike Rapoport <rppt@kernel.org> Cc: Nico Pache <npache@redhat.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Shuang Zhai <zhais@google.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Shuang Zhai <szhai2@cs.rochester.edu> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_KHUGEPAGED_H
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#define _LINUX_KHUGEPAGED_H
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#include <linux/sched/coredump.h> /* MMF_VM_HUGEPAGE */
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extern unsigned int khugepaged_max_ptes_none __read_mostly;
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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extern struct attribute_group khugepaged_attr_group;
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extern int khugepaged_init(void);
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extern void khugepaged_destroy(void);
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extern int start_stop_khugepaged(void);
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extern void __khugepaged_enter(struct mm_struct *mm);
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extern void __khugepaged_exit(struct mm_struct *mm);
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extern void khugepaged_enter_vma(struct vm_area_struct *vma,
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unsigned long vm_flags);
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extern void khugepaged_min_free_kbytes_update(void);
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extern bool current_is_khugepaged(void);
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#ifdef CONFIG_SHMEM
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extern int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
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bool install_pmd);
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#else
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static inline int collapse_pte_mapped_thp(struct mm_struct *mm,
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unsigned long addr, bool install_pmd)
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{
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return 0;
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}
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#endif
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static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
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{
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if (test_bit(MMF_VM_HUGEPAGE, &oldmm->flags))
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__khugepaged_enter(mm);
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}
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static inline void khugepaged_exit(struct mm_struct *mm)
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{
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if (test_bit(MMF_VM_HUGEPAGE, &mm->flags))
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__khugepaged_exit(mm);
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}
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#else /* CONFIG_TRANSPARENT_HUGEPAGE */
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static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
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{
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}
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static inline void khugepaged_exit(struct mm_struct *mm)
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{
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}
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static inline void khugepaged_enter_vma(struct vm_area_struct *vma,
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unsigned long vm_flags)
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{
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}
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static inline int collapse_pte_mapped_thp(struct mm_struct *mm,
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unsigned long addr, bool install_pmd)
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{
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return 0;
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}
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static inline void khugepaged_min_free_kbytes_update(void)
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{
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}
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static inline bool current_is_khugepaged(void)
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{
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return false;
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}
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#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
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#endif /* _LINUX_KHUGEPAGED_H */
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