On Wed, May 4, 2022 at 2:45 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > This idea was introduced by David Rientjes[1]. > > 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 > > An immediate user of this new functionality are 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 THPs to regain > hugepage coverage and dTLB performance. TCMalloc is such an > implementation that could benefit from this[2]. > > Only privately-mapped anon memory is supported for now, but it is > expected that file and shmem support will be added later to support the > use-case of backing executable text by THPs. Current support provided > by CONFIG_READ_ONLY_THP_FOR_FS may take a long time on a large system > which might impair services from serving at their full rated load after > (re)starting. Tricks like mremap(2)'ing text onto anonymous memory to > immediately realize iTLB performance prevents page sharing and demand > paging, both of which increase steady state memory footprint. With > MADV_COLLAPSE, we get the best of both worlds: Peak upfront performance > and lower RAM footprints. > > This call respects THP eligibility as determined by the system-wide > /sys/kernel/mm/transparent_hugepage/enabled sysfs settings and the VMA > flags for the memory range being collapsed. > > THP allocation may enter direct reclaim and/or compaction. > > [1] https://lore.kernel.org/linux-mm/d098c392-273a-36a4-1a29-59731cdf5d3d@xxxxxxxxxx/ > [2] https://github.com/google/tcmalloc/tree/master/tcmalloc > > Suggested-by: David Rientjes <rientjes@xxxxxxxxxx> > Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx> > --- > 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 | 167 +++++++++++++++++++++++-- > mm/madvise.c | 5 + > 8 files changed, 182 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 9a26bd10e083..4a2ea1b5437c 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -222,6 +222,9 @@ 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); > @@ -378,6 +381,15 @@ 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 b14807b7002e..165c646ddb8f 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -837,6 +837,22 @@ static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void) > return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT; > } > > +static bool alloc_hpage(gfp_t gfp, int node, struct collapse_control *cc) > +{ > + 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 false; > + } > + > + prep_transhuge_page(cc->hpage); > + count_vm_event(THP_COLLAPSE_ALLOC); > + return true; > +} > + > #ifdef CONFIG_NUMA > static int khugepaged_find_target_node(struct collapse_control *cc) > { > @@ -882,18 +898,7 @@ static bool khugepaged_prealloc_page(struct page **hpage, bool *wait) > static bool khugepaged_alloc_page(gfp_t gfp, int node, > struct collapse_control *cc) > { > - 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 false; > - } > - > - prep_transhuge_page(cc->hpage); > - count_vm_event(THP_COLLAPSE_ALLOC); > - return true; > + return alloc_hpage(gfp, node, cc); > } > #else > static int khugepaged_find_target_node(struct collapse_control *cc) > @@ -2457,3 +2462,141 @@ 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; > + } > +} > + > +static int madvise_alloc_charge_hpage(struct mm_struct *mm, > + struct collapse_control *cc) > +{ > + if (!alloc_hpage(GFP_TRANSHUGE, khugepaged_find_target_node(cc), cc)) > + return SCAN_ALLOC_HUGE_PAGE_FAIL; > + if (unlikely(mem_cgroup_charge(page_folio(cc->hpage), mm, > + GFP_TRANSHUGE))) > + return SCAN_CGROUP_CHARGE_FAIL; > + count_memcg_page_event(cc->hpage, THP_COLLAPSE_ALLOC); > + return SCAN_SUCCEED; > +} > + > +int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, > + unsigned long start, unsigned long end) > +{ > + struct collapse_control cc = { > + .enforce_pte_scan_limits = false, > + .enforce_young = false, > + .last_target_node = NUMA_NO_NODE, > + .hpage = NULL, > + .alloc_charge_hpage = &madvise_alloc_charge_hpage, > + }; > + struct mm_struct *mm = vma->vm_mm; > + unsigned long hstart, hend, addr; > + int thps = 0, nr_hpages = 0, result = SCAN_FAIL; > + bool mmap_locked = true; > + > + 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(); > + result = SCAN_FAIL; > + Made a last minute change to khugepaged_scan_pmd() which no longer cleared mmap_locked, so it needs to be reset here. Sorry about that - testing was only collapsing 1 huge page so it wasn't caught. > + if (unlikely(khugepaged_test_exit(mm))) { > + result = SCAN_ANY_PROCESS; > + break; > + } > + > + memset(cc.node_load, 0, sizeof(cc.node_load)); > + result = khugepaged_scan_pmd(mm, vma, addr, &mmap_locked, &cc); > + if (!mmap_locked) > + *prev = NULL; /* tell madvise we dropped mmap_lock */ > + > + switch (result) { > + /* Whitelisted set of results where continuing OK */ > + case SCAN_SUCCEED: > + case SCAN_PMD_MAPPED: > + ++thps; > + fallthrough; > + 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 (!mmap_locked) { > + mmap_read_lock(mm); > + mmap_locked = true; > + result = hugepage_vma_revalidate(mm, addr, &vma); > + if (result) > + goto out; > + } > + madvise_collapse_cleanup_page(&cc.hpage); > + } > + > +break_loop: > + /* madvise_walk_vmas() expects us to hold mmap_lock on return */ > + if (!mmap_locked) > + 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(result); > +} > diff --git a/mm/madvise.c b/mm/madvise.c > index 5f4537511532..638517952bd2 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 */ > @@ -1054,6 +1055,8 @@ 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); > @@ -1147,6 +1150,7 @@ 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: > @@ -1336,6 +1340,7 @@ 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. > -- > 2.36.0.464.gb9c8b46e94-goog >
