This idea was introduced by David Rientjes[1], and the semantics and implementation were introduced and discussed in a previous PATCH RFC[2]. Introduce a new madvise mode, MADV_COLLAPSE, that allows users to request a synchronous collapse of memory at their own expense. The benefits of this approach are: * CPU is charged to the process that wants to spend the cycles for the THP * avoid unpredictable timing of khugepaged collapse Immediate users of this new functionality include: * immediately back executable text by hugepages. Current support provided by CONFIG_READ_ONLY_THP_FOR_FS may take too long on a large system. * malloc implementations that manage memory in hugepage-sized chunks, but sometimes subrelease memory back to the system in native-sized chunks via MADV_DONTNEED; zapping the pmd. Later, when the memory is hot, the implementation could madvise(MADV_COLLAPSE) to re-back the memory by THP to regain TLB performance. Allocation semantics are the same as khugepaged, and depend on (1) the active sysfs settings /sys/kernel/mm/transparent_hugepage/enabled and /sys/kernel/mm/transparent_hugepage/khugepaged/defrag, and (2) the VMA flags of the memory range being collapsed. Only privately-mapped anon memory is supported for now. [1] https://lore.kernel.org/linux-mm/d098c392-273a-36a4-1a29-59731cdf5d3d@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/20220308213417.1407042-1-zokeefe@xxxxxxxxxx/ Suggested-by: David Rientjes <rientjes@xxxxxxxxxx> Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx> Reported-by: kernel test robot <lkp@xxxxxxxxx> --- arch/alpha/include/uapi/asm/mman.h | 2 + arch/mips/include/uapi/asm/mman.h | 2 + arch/parisc/include/uapi/asm/mman.h | 2 + arch/xtensa/include/uapi/asm/mman.h | 2 + include/linux/huge_mm.h | 12 ++ include/uapi/asm-generic/mman-common.h | 2 + mm/khugepaged.c | 149 +++++++++++++++++++++++-- mm/madvise.c | 5 + 8 files changed, 164 insertions(+), 12 deletions(-) diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h index 4aa996423b0d..763929e814e9 100644 --- a/arch/alpha/include/uapi/asm/mman.h +++ b/arch/alpha/include/uapi/asm/mman.h @@ -76,6 +76,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h index 1be428663c10..c6e1fc77c996 100644 --- a/arch/mips/include/uapi/asm/mman.h +++ b/arch/mips/include/uapi/asm/mman.h @@ -103,6 +103,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h index a7ea3204a5fa..22133a6a506e 100644 --- a/arch/parisc/include/uapi/asm/mman.h +++ b/arch/parisc/include/uapi/asm/mman.h @@ -70,6 +70,8 @@ #define MADV_WIPEONFORK 71 /* Zero memory on fork, child only */ #define MADV_KEEPONFORK 72 /* Undo MADV_WIPEONFORK */ +#define MADV_COLLAPSE 73 /* Synchronous hugepage collapse */ + #define MADV_HWPOISON 100 /* poison a page for testing */ #define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */ diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h index 7966a58af472..1ff0c858544f 100644 --- a/arch/xtensa/include/uapi/asm/mman.h +++ b/arch/xtensa/include/uapi/asm/mman.h @@ -111,6 +111,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 816a9937f30e..ddad7c7af44e 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -236,6 +236,9 @@ void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud, int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice); +int madvise_collapse(struct vm_area_struct *vma, + struct vm_area_struct **prev, + unsigned long start, unsigned long end); void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, unsigned long end, long adjust_next); spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma); @@ -392,6 +395,15 @@ static inline int hugepage_madvise(struct vm_area_struct *vma, BUG(); return 0; } + +static inline int madvise_collapse(struct vm_area_struct *vma, + struct vm_area_struct **prev, + unsigned long start, unsigned long end) +{ + BUG(); + return 0; +} + static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, unsigned long end, diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h index 6c1aa92a92e4..6ce1f1ceb432 100644 --- a/include/uapi/asm-generic/mman-common.h +++ b/include/uapi/asm-generic/mman-common.h @@ -77,6 +77,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/mm/khugepaged.c b/mm/khugepaged.c index e330a95a0479..c745829c3965 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -846,6 +846,23 @@ static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void) return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT; } +static struct page *alloc_hpage(struct collapse_control *cc, gfp_t gfp, + int node) +{ + VM_BUG_ON_PAGE(cc->hpage, cc->hpage); + + cc->hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER); + if (unlikely(!cc->hpage)) { + count_vm_event(THP_COLLAPSE_ALLOC_FAILED); + cc->hpage = ERR_PTR(-ENOMEM); + return NULL; + } + + prep_transhuge_page(cc->hpage); + count_vm_event(THP_COLLAPSE_ALLOC); + return cc->hpage; +} + #ifdef CONFIG_NUMA static int khugepaged_find_target_node(struct collapse_control *cc) { @@ -892,18 +909,7 @@ static bool khugepaged_prealloc_page(struct page **hpage, bool *wait) static struct page *khugepaged_alloc_page(struct collapse_control *cc, gfp_t gfp, int node) { - VM_BUG_ON_PAGE(cc->hpage, cc->hpage); - - cc->hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER); - if (unlikely(!cc->hpage)) { - count_vm_event(THP_COLLAPSE_ALLOC_FAILED); - cc->hpage = ERR_PTR(-ENOMEM); - return NULL; - } - - prep_transhuge_page(cc->hpage); - count_vm_event(THP_COLLAPSE_ALLOC); - return cc->hpage; + return alloc_hpage(cc, gfp, node); } #else static int khugepaged_find_target_node(struct collapse_control *cc) @@ -2469,3 +2475,122 @@ void khugepaged_min_free_kbytes_update(void) set_recommended_min_free_kbytes(); mutex_unlock(&khugepaged_mutex); } + +static void madvise_collapse_cleanup_page(struct page **hpage) +{ + if (!IS_ERR(*hpage) && *hpage) + put_page(*hpage); + *hpage = NULL; +} + +static int madvise_collapse_errno(enum scan_result r) +{ + switch (r) { + case SCAN_PMD_NULL: + case SCAN_ADDRESS_RANGE: + case SCAN_VMA_NULL: + case SCAN_PTE_NON_PRESENT: + case SCAN_PAGE_NULL: + /* + * Addresses in the specified range are not currently mapped, + * or are outside the AS of the process. + */ + return -ENOMEM; + case SCAN_ALLOC_HUGE_PAGE_FAIL: + case SCAN_CGROUP_CHARGE_FAIL: + /* A kernel resource was temporarily unavailable. */ + return -EAGAIN; + default: + return -EINVAL; + } +} + +int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, + unsigned long start, unsigned long end) +{ + struct collapse_control cc = { + .last_target_node = NUMA_NO_NODE, + .hpage = NULL, + .alloc_hpage = &alloc_hpage, + }; + struct mm_struct *mm = vma->vm_mm; + struct collapse_result cr; + unsigned long hstart, hend, addr; + int thps = 0, nr_hpages = 0; + + BUG_ON(vma->vm_start > start); + BUG_ON(vma->vm_end < end); + + *prev = vma; + + if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) + return -EINVAL; + + hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; + hend = end & HPAGE_PMD_MASK; + nr_hpages = (hend - hstart) >> HPAGE_PMD_SHIFT; + + if (hstart >= hend || !transparent_hugepage_active(vma)) + return -EINVAL; + + mmgrab(mm); + lru_add_drain(); + + for (addr = hstart; ; ) { + mmap_assert_locked(mm); + cond_resched(); + memset(&cr, 0, sizeof(cr)); + + if (unlikely(khugepaged_test_exit(mm))) + break; + + memset(cc.node_load, 0, sizeof(cc.node_load)); + khugepaged_scan_pmd(mm, vma, addr, &cc, &cr); + if (cr.dropped_mmap_lock) + *prev = NULL; /* tell madvise we dropped mmap_lock */ + + switch (cr.result) { + /* Whitelisted set of results where continuing OK */ + case SCAN_SUCCEED: + case SCAN_PMD_MAPPED: + ++thps; + case SCAN_PMD_NULL: + case SCAN_PTE_NON_PRESENT: + case SCAN_PTE_UFFD_WP: + case SCAN_PAGE_RO: + case SCAN_LACK_REFERENCED_PAGE: + case SCAN_PAGE_NULL: + case SCAN_PAGE_COUNT: + case SCAN_PAGE_LOCK: + case SCAN_PAGE_COMPOUND: + break; + case SCAN_PAGE_LRU: + lru_add_drain_all(); + goto retry; + default: + /* Other error, exit */ + goto break_loop; + } + addr += HPAGE_PMD_SIZE; + if (addr >= hend) + break; +retry: + if (cr.dropped_mmap_lock) { + mmap_read_lock(mm); + if (hugepage_vma_revalidate(mm, addr, &vma)) + goto out; + } + madvise_collapse_cleanup_page(&cc.hpage); + } + +break_loop: + /* madvise_walk_vmas() expects us to hold mmap_lock on return */ + if (cr.dropped_mmap_lock) + mmap_read_lock(mm); +out: + mmap_assert_locked(mm); + madvise_collapse_cleanup_page(&cc.hpage); + mmdrop(mm); + + return thps == nr_hpages ? 0 : madvise_collapse_errno(cr.result); +} diff --git a/mm/madvise.c b/mm/madvise.c index ec03a76244b7..7ad53e5311cf 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -59,6 +59,7 @@ static int madvise_need_mmap_write(int behavior) case MADV_FREE: case MADV_POPULATE_READ: case MADV_POPULATE_WRITE: + case MADV_COLLAPSE: return 0; default: /* be safe, default to 1. list exceptions explicitly */ @@ -1051,6 +1052,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, if (error) goto out; break; + case MADV_COLLAPSE: + return madvise_collapse(vma, prev, start, end); } anon_name = anon_vma_name(vma); @@ -1144,6 +1147,7 @@ madvise_behavior_valid(int behavior) #ifdef CONFIG_TRANSPARENT_HUGEPAGE case MADV_HUGEPAGE: case MADV_NOHUGEPAGE: + case MADV_COLLAPSE: #endif case MADV_DONTDUMP: case MADV_DODUMP: @@ -1333,6 +1337,7 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, * MADV_NOHUGEPAGE - mark the given range as not worth being backed by * transparent huge pages so the existing pages will not be * coalesced into THP and new pages will not be allocated as THP. + * MADV_COLLAPSE - synchronously coalesce pages into new THP. * MADV_DONTDUMP - the application wants to prevent pages in the given range * from being included in its core dump. * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump. -- 2.36.0.rc0.470.gd361397f0d-goog
