On 10/29/2015 10:55 PM, Shaohua Li wrote:
> In jemalloc, a free(3) doesn't immediately free the memory to OS even
> the memory is page aligned/size, and hope the memory can be reused soon.
> Later the virtual address becomes fragmented, and more and more free
> memory are aggregated. If the free memory size is large, jemalloc uses
> madvise(DONT_NEED) to actually free the memory back to OS.
>
> The madvise has significantly overhead paritcularly because of TLB
> flush. jemalloc does madvise for several virtual address space ranges
> one time. Instead of calling madvise for each of the ranges, we
> introduce a new syscall to purge memory for several ranges one time. In
> this way, we can merge several TLB flush for the ranges to one big TLB
> flush. This also reduce mmap_sem locking.
>
> I'm running a simple memory allocation benchmark. 32 threads do random
> malloc/free/realloc. Corresponding jemalloc patch to utilize this API is
> attached.
> Without patch:
> real 0m18.923s
> user 1m11.819s
> sys 7m44.626s
> each cpu gets around 3000K/s TLB flush interrupt. Perf shows TLB flush
> is hotest functions. mmap_sem read locking (because of page fault) is
> also heavy.
>
> with patch:
> real 0m15.026s
> user 0m48.548s
> sys 6m41.153s
> each cpu gets around 140k/s TLB flush interrupt. TLB flush isn't hot at
> all. mmap_sem read locking (still because of page fault) becomes the
> sole hot spot.
>
> Another test malloc a bunch of memory in 48 threads, then all threads
> free the memory. I measure the time of the memory free.
> Without patch: 34.332s
> With patch: 17.429s
>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: Mel Gorman <mgor...@suse.de>
> Cc: Hugh Dickins <hu...@google.com>
> Cc: Johannes Weiner <han...@cmpxchg.org>
> Cc: Andrea Arcangeli <aarca...@redhat.com>
> Signed-off-by: Shaohua Li <s...@fb.com>
First the obligatory (please remember on next submissions):
[CC += linux-api@vger.kernel.org]
Since this is a kernel-user-space API change, please CC linux-api@. The
kernel source file Documentation/SubmitChecklist notes that all Linux kernel
patches that change userspace interfaces should be CCed to
linux-api@vger.kernel.org, so that the various parties who are interested in API
changes are informed. For further information, see
https://www.kernel.org/doc/man-pages/linux-api-ml.html
Also CCing Minchan. What about MADV_FREE support?
> ---
> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> mm/madvise.c | 144
> ++++++++++++++++++++++++++++++---
> 3 files changed, 134 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl
> b/arch/x86/entry/syscalls/syscall_32.tbl
> index 7663c45..4c99ef5 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -382,3 +382,4 @@
> 373 i386 shutdown sys_shutdown
> 374 i386 userfaultfd sys_userfaultfd
> 375 i386 membarrier sys_membarrier
> +376 i386 madvisev sys_madvisev
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl
> b/arch/x86/entry/syscalls/syscall_64.tbl
> index 278842f..1025406 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -331,6 +331,7 @@
> 322 64 execveat stub_execveat
> 323 common userfaultfd sys_userfaultfd
> 324 common membarrier sys_membarrier
> +325 common madvisev sys_madvisev
>
> #
> # x32-specific system call numbers start at 512 to avoid cache impact
> diff --git a/mm/madvise.c b/mm/madvise.c
> index c889fcb..6251103 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -20,6 +20,9 @@
> #include <linux/backing-dev.h>
> #include <linux/swap.h>
> #include <linux/swapops.h>
> +#include <linux/uio.h>
> +#include <linux/sort.h>
> +#include <asm/tlb.h>
>
> /*
> * Any behaviour which results in changes to the vma->vm_flags needs to
> @@ -415,6 +418,29 @@ madvise_behavior_valid(int behavior)
> }
> }
>
> +static bool madvise_range_valid(unsigned long start, size_t len_in, bool
> *skip)
> +{
> + size_t len;
> + unsigned long end;
> +
> + if (start & ~PAGE_MASK)
> + return false;
> + len = (len_in + ~PAGE_MASK) & PAGE_MASK;
> +
> + /* Check to see whether len was rounded up from small -ve to zero */
> + if (len_in && !len)
> + return false;
> +
> + end = start + len;
> + if (end < start)
> + return false;
> + if (end == start)
> + *skip = true;
> + else
> + *skip = false;
> + return true;
> +}
> +
> /*
> * The madvise(2) system call.
> *
> @@ -464,8 +490,8 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t,
> len_in, int, behavior)
> int unmapped_error = 0;
> int error = -EINVAL;
> int write;
> - size_t len;
> struct blk_plug plug;
> + bool skip;
>
> #ifdef CONFIG_MEMORY_FAILURE
> if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
> @@ -474,20 +500,12 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t,
> len_in, int, behavior)
> if (!madvise_behavior_valid(behavior))
> return error;
>
> - if (start & ~PAGE_MASK)
> - return error;
> - len = (len_in + ~PAGE_MASK) & PAGE_MASK;
> -
> - /* Check to see whether len was rounded up from small -ve to zero */
> - if (len_in && !len)
> - return error;
> -
> - end = start + len;
> - if (end < start)
> + if (!madvise_range_valid(start, len_in, &skip))
> return error;
> + end = start + ((len_in + ~PAGE_MASK) & PAGE_MASK);
>
> error = 0;
> - if (end == start)
> + if (skip)
> return error;
>
> write = madvise_need_mmap_write(behavior);
> @@ -549,3 +567,105 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t,
> len_in, int, behavior)
>
> return error;
> }
> +
> +static int iov_cmp_func(const void *a, const void *b)
> +{
> + const struct iovec *iova = a;
> + const struct iovec *iovb = b;
> + unsigned long addr_a = (unsigned long)iova->iov_base;
> + unsigned long addr_b = (unsigned long)iovb->iov_base;
> +
> + if (addr_a > addr_b)
> + return 1;
> + if (addr_a < addr_b)
> + return -1;
> + return 0;
> +}
> +
> +SYSCALL_DEFINE3(madvisev, const struct iovec __user *, uvector, unsigned
> long, nr_segs,
> + int, behavior)
> +{
> + struct iovec iovstack[UIO_FASTIOV];
> + struct iovec *iov = NULL;
> + struct vm_area_struct **vmas = NULL;
> + unsigned long start, last_start = 0;
> + size_t len;
> + struct mmu_gather tlb;
> + int error;
> + int i;
> + bool skip;
> +
> + if (behavior != MADV_DONTNEED)
> + return -EINVAL;
> +
> + error = rw_copy_check_uvector(CHECK_IOVEC_ONLY, uvector, nr_segs,
> + UIO_FASTIOV, iovstack, &iov);
> + if (error <= 0)
> + return error;
> + /* Make sure address in ascend order */
> + sort(iov, nr_segs, sizeof(struct iovec), iov_cmp_func, NULL);
> +
> + vmas = kmalloc(nr_segs * sizeof(struct vm_area_struct *), GFP_KERNEL);
> + if (!vmas) {
> + error = -EFAULT;
> + goto out;
> + }
> + for (i = 0; i < nr_segs; i++) {
> + start = (unsigned long)iov[i].iov_base;
> + len = ((iov[i].iov_len + ~PAGE_MASK) & PAGE_MASK);
> + iov[i].iov_len = len;
> + if (start < last_start) {
> + error = -EINVAL;
> + goto out;
> + }
> + if (!madvise_range_valid(start, len, &skip)) {
> + error = -EINVAL;
> + goto out;
> + }
> + if (skip) {
> + error = 0;
> + goto out;
> + }
> + last_start = start + len;
> + }
> +
> + down_read(¤t->mm->mmap_sem);
> + for (i = 0; i < nr_segs; i++) {
> + start = (unsigned long)iov[i].iov_base;
> + len = iov[i].iov_len;
> + vmas[i] = find_vma(current->mm, start);
> + /*
> + * don't allow range cross vma, it doesn't make sense for
> + * DONTNEED
> + */
> + if (!vmas[i] || start < vmas[i]->vm_start ||
> + start + len > vmas[i]->vm_end) {
> + error = -ENOMEM;
> + goto up_out;
> + }
> + if (vmas[i]->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP)) {
> + error = -EINVAL;
> + goto up_out;
> + }
> + }
> +
> + lru_add_drain();
> + tlb_gather_mmu(&tlb, current->mm, (unsigned long)iov[0].iov_base,
> + last_start);
> + update_hiwater_rss(current->mm);
> + for (i = 0; i < nr_segs; i++) {
> + start = (unsigned long)iov[i].iov_base;
> + len = iov[i].iov_len;
> + unmap_vmas(&tlb, vmas[i], start, start + len);
> + }
> + tlb_finish_mmu(&tlb, (unsigned long)iov[0].iov_base, last_start);
> + error = 0;
> +
> +up_out:
> + up_read(¤t->mm->mmap_sem);
> +out:
> + kfree(vmas);
> + if (iov != iovstack)
> + kfree(iov);
> + return error;
> +}
>
>
> je.patch
>
>
> diff --git a/src/arena.c b/src/arena.c
> index 43733cc..ae2de35 100644
> --- a/src/arena.c
> +++ b/src/arena.c
> @@ -1266,6 +1266,7 @@ arena_dirty_count(arena_t *arena)
> return (ndirty);
> }
>
> +#define PURGE_VEC 1
> static size_t
> arena_compute_npurge(arena_t *arena, bool all)
> {
> @@ -1280,6 +1281,10 @@ arena_compute_npurge(arena_t *arena, bool all)
> threshold = threshold < chunk_npages ? chunk_npages : threshold;
>
> npurge = arena->ndirty - threshold;
> +#if PURGE_VEC
> + if (npurge < arena->ndirty / 2)
> + npurge = arena->ndirty / 2;
> +#endif
> } else
> npurge = arena->ndirty;
>
> @@ -1366,6 +1371,16 @@ arena_stash_dirty(arena_t *arena, chunk_hooks_t
> *chunk_hooks, bool all,
> return (nstashed);
> }
>
> +#if PURGE_VEC
> +#define MAX_IOVEC 32
> +bool pages_purge_vec(struct iovec *iov, unsigned long nr_segs)
> +{
> + int ret = syscall(325, iov, nr_segs, MADV_DONTNEED);
> +
> + return !!ret;
> +}
> +#endif
> +
> static size_t
> arena_purge_stashed(arena_t *arena, chunk_hooks_t *chunk_hooks,
> arena_runs_dirty_link_t *purge_runs_sentinel,
> @@ -1374,6 +1389,10 @@ arena_purge_stashed(arena_t *arena, chunk_hooks_t
> *chunk_hooks,
> size_t npurged, nmadvise;
> arena_runs_dirty_link_t *rdelm;
> extent_node_t *chunkselm;
> +#if PURGE_VEC
> + struct iovec iovec[MAX_IOVEC];
> + int vec_index = 0;
> +#endif
>
> if (config_stats)
> nmadvise = 0;
> @@ -1418,9 +1437,21 @@ arena_purge_stashed(arena_t *arena, chunk_hooks_t
> *chunk_hooks,
> flag_unzeroed = 0;
> flags = CHUNK_MAP_DECOMMITTED;
> } else {
> +#if !PURGE_VEC
> flag_unzeroed = chunk_purge_wrapper(arena,
> chunk_hooks, chunk, chunksize, pageind <<
> LG_PAGE, run_size) ? CHUNK_MAP_UNZEROED : 0;
> +#else
> + flag_unzeroed = 0;
> + iovec[vec_index].iov_base = (void
> *)((uintptr_t)chunk +
> + (pageind << LG_PAGE));
> + iovec[vec_index].iov_len = run_size;
> + vec_index++;
> + if (vec_index >= MAX_IOVEC) {
> + pages_purge_vec(iovec, vec_index);
> + vec_index = 0;
> + }
> +#endif
> flags = flag_unzeroed;
> }
> arena_mapbits_large_set(chunk, pageind+npages-1, 0,
> @@ -1449,6 +1480,10 @@ arena_purge_stashed(arena_t *arena, chunk_hooks_t
> *chunk_hooks,
> if (config_stats)
> nmadvise++;
> }
> +#if PURGE_VEC
> + if (vec_index > 0)
> + pages_purge_vec(iovec, vec_index);
> +#endif
> malloc_mutex_lock(&arena->lock);
>
> if (config_stats) {
>
--
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