[CC linux-api] On Thu 18-01-24 20:03:46, Lance Yang wrote: > This idea was inspired by MADV_COLLAPSE introduced by Zach O'Keefe[1]. > > Allow MADV_F_COLLAPSE_LIGHT behavior for process_madvise(2) if the caller > has CAP_SYS_ADMIN or is requesting the collapse of its own memory. > > The semantics of MADV_F_COLLAPSE_LIGHT are similar to MADV_COLLAPSE, but > it avoids direct reclaim and/or compaction, quickly failing on allocation > errors. > > This change enables a more flexible and efficient usage of memory collapse > operations, providing additional control to userspace applications for > system-wide THP optimization. > > Semantics > > This call is independent of the system-wide THP sysfs settings, but will > fail for memory marked VM_NOHUGEPAGE. If the ranges provided span > multiple VMAs, the semantics of the collapse over each VMA is independent > from the others. This implies a hugepage cannot cross a VMA boundary. If > collapse of a given hugepage-aligned/sized region fails, the operation may > continue to attempt collapsing the remainder of memory specified. > > The memory ranges provided must be page-aligned, but are not required to > be hugepage-aligned. If the memory ranges are not hugepage-aligned, the > start/end of the range will be clamped to the first/last hugepage-aligned > address covered by said range. The memory ranges must span at least one > hugepage-sized region. > > All non-resident pages covered by the range will first be > swapped/faulted-in, before being internally copied onto a freshly > allocated hugepage. Unmapped pages will have their data directly > initialized to 0 in the new hugepage. However, for every eligible > hugepage aligned/sized region to-be collapsed, at least one page must > currently be backed by memory (a PMD covering the address range must > already exist). > > Allocation for the new hugepage will not enter direct reclaim and/or > compaction, quickly failing if allocation fails. When the system has > multiple NUMA nodes, the hugepage will be allocated from the node providing > the most native pages. This operation operates on the current state of the > specified process and makes no persistent changes or guarantees on how pages > will be mapped, constructed, or faulted in the future. > > Use Cases > > An immediate user of this new functionality is the Go runtime heap allocator > that manages memory in hugepage-sized chunks. In the past, whether it was a > newly allocated chunk through mmap() or a reused chunk released by > madvise(MADV_DONTNEED), the allocator attempted to eagerly back memory with > huge pages using madvise(MADV_HUGEPAGE)[2] and madvise(MADV_COLLAPSE)[3] > respectively. However, both approaches resulted in performance issues; for > both scenarios, there could be entries into direct reclaim and/or compaction, > leading to unpredictable stalls[4]. Now, the allocator can confidently use > process_madvise(MADV_F_COLLAPSE_LIGHT) to attempt the allocation of huge pages. > > [1] https://github.com/torvalds/linux/commit/7d8faaf155454f8798ec56404faca29a82689c77 > [2] https://github.com/golang/go/commit/8fa9e3beee8b0e6baa7333740996181268b60a3a > [3] https://github.com/golang/go/commit/9f9bb26880388c5bead158e9eca3be4b3a9bd2af > [4] https://github.com/golang/go/issues/63334 > > [v1] https://lore.kernel.org/lkml/20240117050217.43610-1-ioworker0@xxxxxxxxx/ > > Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx> > Suggested-by: Zach O'Keefe <zokeefe@xxxxxxxxxx> > Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > --- > V1 -> V2: Treat process_madvise(MADV_F_COLLAPSE_LIGHT) as the lighter-weight alternative > to madvise(MADV_COLLAPSE) > > arch/alpha/include/uapi/asm/mman.h | 1 + > arch/mips/include/uapi/asm/mman.h | 1 + > arch/parisc/include/uapi/asm/mman.h | 1 + > arch/xtensa/include/uapi/asm/mman.h | 1 + > include/linux/huge_mm.h | 5 +-- > include/uapi/asm-generic/mman-common.h | 1 + > mm/khugepaged.c | 15 ++++++-- > mm/madvise.c | 36 +++++++++++++++++--- > tools/include/uapi/asm-generic/mman-common.h | 1 + > 9 files changed, 52 insertions(+), 10 deletions(-) > > diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h > index 763929e814e9..22f23ca04f1a 100644 > --- a/arch/alpha/include/uapi/asm/mman.h > +++ b/arch/alpha/include/uapi/asm/mman.h > @@ -77,6 +77,7 @@ > #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > +#define MADV_F_COLLAPSE_LIGHT 26 /* Similar to COLLAPSE, but avoids direct reclaim and/or compaction */ > > /* 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 c6e1fc77c996..acec0b643e9c 100644 > --- a/arch/mips/include/uapi/asm/mman.h > +++ b/arch/mips/include/uapi/asm/mman.h > @@ -104,6 +104,7 @@ > #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > +#define MADV_F_COLLAPSE_LIGHT 26 /* Similar to COLLAPSE, but avoids direct reclaim and/or compaction */ > > /* 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 68c44f99bc93..812029c98cd7 100644 > --- a/arch/parisc/include/uapi/asm/mman.h > +++ b/arch/parisc/include/uapi/asm/mman.h > @@ -71,6 +71,7 @@ > #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > +#define MADV_F_COLLAPSE_LIGHT 26 /* Similar to COLLAPSE, but avoids direct reclaim and/or compaction */ > > #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 1ff0c858544f..52ef463dd5b6 100644 > --- a/arch/xtensa/include/uapi/asm/mman.h > +++ b/arch/xtensa/include/uapi/asm/mman.h > @@ -112,6 +112,7 @@ > #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > +#define MADV_F_COLLAPSE_LIGHT 26 /* Similar to COLLAPSE, but avoids direct reclaim and/or compaction */ > > /* compatibility flags */ > #define MAP_FILE 0 > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 5adb86af35fc..075fdb5d481a 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -303,7 +303,7 @@ 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); > + unsigned long start, unsigned long end, int behavior); > 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); > @@ -450,7 +450,8 @@ static inline int hugepage_madvise(struct vm_area_struct *vma, > > static inline int madvise_collapse(struct vm_area_struct *vma, > struct vm_area_struct **prev, > - unsigned long start, unsigned long end) > + unsigned long start, unsigned long end, > + int behavior) > { > return -EINVAL; > } > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h > index 6ce1f1ceb432..92c67bc755da 100644 > --- a/include/uapi/asm-generic/mman-common.h > +++ b/include/uapi/asm-generic/mman-common.h > @@ -78,6 +78,7 @@ > #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > +#define MADV_F_COLLAPSE_LIGHT 26 /* Similar to COLLAPSE, but avoids direct reclaim and/or compaction */ > > /* compatibility flags */ > #define MAP_FILE 0 > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 2b219acb528e..2840051c0ae2 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -97,6 +97,8 @@ static struct kmem_cache *mm_slot_cache __ro_after_init; > struct collapse_control { > bool is_khugepaged; > > + int behavior; > + > /* Num pages scanned per node */ > u32 node_load[MAX_NUMNODES]; > > @@ -1058,10 +1060,16 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm, > static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm, > struct collapse_control *cc) > { > - gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() : > - GFP_TRANSHUGE); > int node = hpage_collapse_find_target_node(cc); > struct folio *folio; > + gfp_t gfp; > + > + if (cc->is_khugepaged) > + gfp = alloc_hugepage_khugepaged_gfpmask(); > + else > + gfp = (cc->behavior == MADV_F_COLLAPSE_LIGHT ? > + GFP_TRANSHUGE_LIGHT : > + GFP_TRANSHUGE); > > if (!hpage_collapse_alloc_folio(&folio, gfp, node, &cc->alloc_nmask)) { > *hpage = NULL; > @@ -2697,7 +2705,7 @@ static int madvise_collapse_errno(enum scan_result r) > } > > int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, > - unsigned long start, unsigned long end) > + unsigned long start, unsigned long end, int behavior) > { > struct collapse_control *cc; > struct mm_struct *mm = vma->vm_mm; > @@ -2718,6 +2726,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, > if (!cc) > return -ENOMEM; > cc->is_khugepaged = false; > + cc->behavior = behavior; > > mmgrab(mm); > lru_add_drain_all(); > diff --git a/mm/madvise.c b/mm/madvise.c > index 912155a94ed5..9c40226505aa 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -60,6 +60,7 @@ static int madvise_need_mmap_write(int behavior) > case MADV_POPULATE_READ: > case MADV_POPULATE_WRITE: > case MADV_COLLAPSE: > + case MADV_F_COLLAPSE_LIGHT: > return 0; > default: > /* be safe, default to 1. list exceptions explicitly */ > @@ -1082,8 +1083,9 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, > if (error) > goto out; > break; > + case MADV_F_COLLAPSE_LIGHT: > case MADV_COLLAPSE: > - return madvise_collapse(vma, prev, start, end); > + return madvise_collapse(vma, prev, start, end, behavior); > } > > anon_name = anon_vma_name(vma); > @@ -1178,6 +1180,7 @@ madvise_behavior_valid(int behavior) > case MADV_HUGEPAGE: > case MADV_NOHUGEPAGE: > case MADV_COLLAPSE: > + case MADV_F_COLLAPSE_LIGHT: > #endif > case MADV_DONTDUMP: > case MADV_DODUMP: > @@ -1194,6 +1197,17 @@ madvise_behavior_valid(int behavior) > } > } > > + > +static bool process_madvise_behavior_only(int behavior) > +{ > + switch (behavior) { > + case MADV_F_COLLAPSE_LIGHT: > + return true; > + default: > + return false; > + } > +} > + > static bool process_madvise_behavior_valid(int behavior) > { > switch (behavior) { > @@ -1201,6 +1215,7 @@ static bool process_madvise_behavior_valid(int behavior) > case MADV_PAGEOUT: > case MADV_WILLNEED: > case MADV_COLLAPSE: > + case MADV_F_COLLAPSE_LIGHT: > return true; > default: > return false; > @@ -1368,6 +1383,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, > * 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_F_COLLAPSE_LIGHT - only for process_madvise, avoids direct reclaim and/or > + * compaction. > * 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. > @@ -1394,7 +1411,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, > * -EBADF - map exists, but area maps something that isn't a file. > * -EAGAIN - a kernel resource was temporarily unavailable. > */ > -int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior) > +int _do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, > + int behavior, bool is_process_madvise) > { > unsigned long end; > int error; > @@ -1405,6 +1423,9 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh > if (!madvise_behavior_valid(behavior)) > return -EINVAL; > > + if (!is_process_madvise && process_madvise_behavior_only(behavior)) > + return -EINVAL; > + > if (!PAGE_ALIGNED(start)) > return -EINVAL; > len = PAGE_ALIGN(len_in); > @@ -1448,9 +1469,14 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh > return error; > } > > +int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior) > +{ > + return _do_madvise(mm, start, len_in, behavior, false); > +} > + > SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior) > { > - return do_madvise(current->mm, start, len_in, behavior); > + return _do_madvise(current->mm, start, len_in, behavior, false); > } > > SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > @@ -1504,8 +1530,8 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec, > total_len = iov_iter_count(&iter); > > while (iov_iter_count(&iter)) { > - ret = do_madvise(mm, (unsigned long)iter_iov_addr(&iter), > - iter_iov_len(&iter), behavior); > + ret = _do_madvise(mm, (unsigned long)iter_iov_addr(&iter), > + iter_iov_len(&iter), behavior, true); > if (ret < 0) > break; > iov_iter_advance(&iter, iter_iov_len(&iter)); > diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h > index 6ce1f1ceb432..92c67bc755da 100644 > --- a/tools/include/uapi/asm-generic/mman-common.h > +++ b/tools/include/uapi/asm-generic/mman-common.h > @@ -78,6 +78,7 @@ > #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ > > #define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ > +#define MADV_F_COLLAPSE_LIGHT 26 /* Similar to COLLAPSE, but avoids direct reclaim and/or compaction */ > > /* compatibility flags */ > #define MAP_FILE 0 > -- > 2.33.1 -- Michal Hocko SUSE Labs
