On Thu, May 5, 2022 at 11:50 AM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > 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. > Please disregard - I reset it at the end of the loop when reacquiring lock ; I did something else silly in a merge. Sorry for the noise. > > + 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 > >
