Ccing relevant folks. On Fri, Jan 10, 2025 at 04:46:18PM -0800, SeongJae Park wrote: > process_madvise() calls do_madvise() for each address range. Then, each > do_madvise() invocation holds and releases same mmap_lock. Optimize the > redundant lock operations by doing the locking in process_madvise(), and > inform do_madvise() that the lock is already held and therefore can be > skipped. > > Evaluation > ========== > > I measured the time to apply MADV_DONTNEED advice to 256 MiB memory > using multiple madvise() calls, 4 KiB per each call. I also do the same > with process_madvise(), but with varying iovec size from 1 to 1024. > The source code for the measurement is available at GitHub[1]. > > The measurement results are as below. 'sz_batches' column shows the > iovec size of process_madvise() calls. '0' is for madvise() calls case. > 'before' and 'after' columns are the measured time to apply > MADV_DONTNEED to the 256 MiB memory buffer in nanoseconds, on kernels > that built without and with this patch, respectively. So lower value > means better efficiency. 'after/before' column is the ratio of 'after' > to 'before'. > > sz_batches before after after/before > 0 124062365 96670188 0.779206393494111 > 1 136341258 113915688 0.835518827323714 > 2 105314942 78898211 0.749164453796119 > 4 82012858 59778998 0.728897875989153 > 8 82562651 51003069 0.617749895167489 > 16 71474930 47575960 0.665631431888076 > 32 71391211 42902076 0.600943385033768 > 64 68225932 41337835 0.605896230190011 > 128 71053578 42467240 0.597679120395598 > 256 85094126 41630463 0.489228398679364 > 512 68531628 44049763 0.6427654542221 > 1024 79338892 43370866 0.546653285755491 > > The measurement shows this patch reduces the process_madvise() latency, > proportional to the batching size, from about 25% with the batch size 2 > to about 55% with the batch size 1,024. The trend is somewhat we can > expect. > > Interestingly, this patch has also optimize madvise() and single batch > size process_madvise(), though. I ran this test multiple times, but the > results are consistent. I'm still investigating if there are something > I'm missing. But I believe the investigation may not necessarily be a > blocker of this RFC, so just posting this. I will add updates of the > madvise() and single batch size process_madvise() investigation later. > > [1] https://github.com/sjp38/eval_proc_madvise > > Signed-off-by: SeongJae Park <sj@xxxxxxxxxx> > --- > include/linux/mm.h | 3 ++- > io_uring/advise.c | 2 +- > mm/damon/vaddr.c | 2 +- > mm/madvise.c | 54 +++++++++++++++++++++++++++++++++++----------- > 4 files changed, 45 insertions(+), 16 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 612b513ebfbd..e3ca5967ebd4 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3459,7 +3459,8 @@ int do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma, > unsigned long end, struct list_head *uf, bool unlock); > extern int do_munmap(struct mm_struct *, unsigned long, size_t, > struct list_head *uf); > -extern int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior); > +extern int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, > + int behavior, bool lock_held); > > #ifdef CONFIG_MMU > extern int __mm_populate(unsigned long addr, unsigned long len, > diff --git a/io_uring/advise.c b/io_uring/advise.c > index cb7b881665e5..010b55d5a26e 100644 > --- a/io_uring/advise.c > +++ b/io_uring/advise.c > @@ -56,7 +56,7 @@ int io_madvise(struct io_kiocb *req, unsigned int issue_flags) > > WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK); > > - ret = do_madvise(current->mm, ma->addr, ma->len, ma->advice); > + ret = do_madvise(current->mm, ma->addr, ma->len, ma->advice, false); > io_req_set_res(req, ret, 0); > return IOU_OK; > #else > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c > index a6174f725bd7..30b5a251d73e 100644 > --- a/mm/damon/vaddr.c > +++ b/mm/damon/vaddr.c > @@ -646,7 +646,7 @@ static unsigned long damos_madvise(struct damon_target *target, > if (!mm) > return 0; > > - applied = do_madvise(mm, start, len, behavior) ? 0 : len; > + applied = do_madvise(mm, start, len, behavior, false) ? 0 : len; > mmput(mm); > > return applied; > diff --git a/mm/madvise.c b/mm/madvise.c > index 49f3a75046f6..c107376db9d5 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1637,7 +1637,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, > * -EAGAIN - a kernel resource was temporarily unavailable. > * -EPERM - memory is sealed. > */ > -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 lock_held) > { > unsigned long end; > int error; > @@ -1668,12 +1669,14 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh > return madvise_inject_error(behavior, start, start + len_in); > #endif > > - write = madvise_need_mmap_write(behavior); > - if (write) { > - if (mmap_write_lock_killable(mm)) > - return -EINTR; > - } else { > - mmap_read_lock(mm); > + if (!lock_held) { > + write = madvise_need_mmap_write(behavior); > + if (write) { > + if (mmap_write_lock_killable(mm)) > + return -EINTR; > + } else { > + mmap_read_lock(mm); > + } > } > > start = untagged_addr_remote(mm, start); > @@ -1692,17 +1695,19 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh > } > blk_finish_plug(&plug); > > - if (write) > - mmap_write_unlock(mm); > - else > - mmap_read_unlock(mm); > + if (!lock_held) { > + if (write) > + mmap_write_unlock(mm); > + else > + mmap_read_unlock(mm); > + } > > return error; > } > > 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); > } > > /* Perform an madvise operation over a vector of addresses and lengths. */ > @@ -1711,12 +1716,28 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter, > { > ssize_t ret = 0; > size_t total_len; > + bool hold_lock = true; > + int write; > > total_len = iov_iter_count(iter); > > +#ifdef CONFIG_MEMORY_FAILURE > + if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE) > + hold_lock = false; > +#endif > + if (hold_lock) { > + write = madvise_need_mmap_write(behavior); > + if (write) { > + if (mmap_write_lock_killable(mm)) > + return -EINTR; > + } else { > + mmap_read_lock(mm); > + } > + } > + > while (iov_iter_count(iter)) { > ret = do_madvise(mm, (unsigned long)iter_iov_addr(iter), > - iter_iov_len(iter), behavior); > + iter_iov_len(iter), behavior, hold_lock); > /* > * An madvise operation is attempting to restart the syscall, > * but we cannot proceed as it would not be correct to repeat > @@ -1739,6 +1760,13 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter, > iov_iter_advance(iter, iter_iov_len(iter)); > } > > + if (hold_lock) { > + if (write) > + mmap_write_unlock(mm); > + else > + mmap_read_unlock(mm); > + } > + > ret = (total_len - iov_iter_count(iter)) ? : ret; > > return ret; > -- > 2.39.5
