Re: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range

[Suren Baghdasaryan <surenb@google.com>]

On Wed, Nov 25, 2020 at 3:13 PM Minchan Kim <minchan@kernel.org> wrote:
>
> On Mon, Nov 23, 2020 at 09:39:42PM -0800, Suren Baghdasaryan wrote:
> > process_madvise requires a vector of address ranges to be provided for
> > its operations. When an advice should be applied to the entire process,
> > the caller process has to obtain the list of VMAs of the target process
> > by reading the /proc/pid/maps or some other way. The cost of this
> > operation grows linearly with increasing number of VMAs in the target
> > process. Even constructing the input vector can be non-trivial when
> > target process has several thousands of VMAs and the syscall is being
> > issued during high memory pressure period when new allocations for such
> > a vector would only worsen the situation.
> > In the case when advice is being applied to the entire memory space of
> > the target process, this creates an extra overhead.
> > Add PMADV_FLAG_RANGE flag for process_madvise enabling the caller to
> > advise a memory range of the target process. For now, to keep it simple,
> > only the entire process memory range is supported, vec and vlen inputs
> > in this mode are ignored and can be NULL and 0.
> > Instead of returning the number of bytes that advice was successfully
> > applied to, the syscall in this mode returns 0 on success. This is due
> > to the fact that the number of bytes would not be useful for the caller
> > that does not know the amount of memory the call is supposed to affect.
> > Besides, the ssize_t return type can be too small to hold the number of
> > bytes affected when the operation is applied to a large memory range.
>
> Can we just use one element in iovec to indicate entire address rather
> than using up the reserved flags?
>
>         struct iovec {
>                 .iov_base = NULL,
>                 .iov_len = (~(size_t)0),
>         };
>
> Furthermore, it would be applied for other syscalls where have support
> iovec if we agree on it.
>

The flag also changes the return value semantics. If we follow your
suggestion we should also agree that in this mode the return value
will be 0 on success and negative otherwise instead of the number of
bytes madvise was applied to.

> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  arch/alpha/include/uapi/asm/mman.h           |  4 ++
> >  arch/mips/include/uapi/asm/mman.h            |  4 ++
> >  arch/parisc/include/uapi/asm/mman.h          |  4 ++
> >  arch/xtensa/include/uapi/asm/mman.h          |  4 ++
> >  fs/io_uring.c                                |  2 +-
> >  include/linux/mm.h                           |  3 +-
> >  include/uapi/asm-generic/mman-common.h       |  4 ++
> >  mm/madvise.c                                 | 47 +++++++++++++++++---
> >  tools/include/uapi/asm-generic/mman-common.h |  4 ++
> >  9 files changed, 67 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
> > index a18ec7f63888..54588d2f5406 100644
> > --- a/arch/alpha/include/uapi/asm/mman.h
> > +++ b/arch/alpha/include/uapi/asm/mman.h
> > @@ -79,4 +79,8 @@
> >  #define PKEY_ACCESS_MASK     (PKEY_DISABLE_ACCESS |\
> >                                PKEY_DISABLE_WRITE)
> >
> > +/* process_madvise flags */
> > +#define PMADV_FLAG_RANGE     0x1     /* advice for all VMAs in the range */
> > +#define PMADV_FLAG_MASK      (PMADV_FLAG_RANGE)
> > +
> >  #endif /* __ALPHA_MMAN_H__ */
> > diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
> > index 57dc2ac4f8bd..af94f38a3a9d 100644
> > --- a/arch/mips/include/uapi/asm/mman.h
> > +++ b/arch/mips/include/uapi/asm/mman.h
> > @@ -106,4 +106,8 @@
> >  #define PKEY_ACCESS_MASK     (PKEY_DISABLE_ACCESS |\
> >                                PKEY_DISABLE_WRITE)
> >
> > +/* process_madvise flags */
> > +#define PMADV_FLAG_RANGE     0x1     /* advice for all VMAs in the range */
> > +#define PMADV_FLAG_MASK      (PMADV_FLAG_RANGE)
> > +
> >  #endif /* _ASM_MMAN_H */
> > diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
> > index ab78cba446ed..ae644c493991 100644
> > --- a/arch/parisc/include/uapi/asm/mman.h
> > +++ b/arch/parisc/include/uapi/asm/mman.h
> > @@ -77,4 +77,8 @@
> >  #define PKEY_ACCESS_MASK     (PKEY_DISABLE_ACCESS |\
> >                                PKEY_DISABLE_WRITE)
> >
> > +/* process_madvise flags */
> > +#define PMADV_FLAG_RANGE     0x1     /* advice for all VMAs in the range */
> > +#define PMADV_FLAG_MASK      (PMADV_FLAG_RANGE)
> > +
> >  #endif /* __PARISC_MMAN_H__ */
> > diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
> > index e5e643752947..934cdd11abff 100644
> > --- a/arch/xtensa/include/uapi/asm/mman.h
> > +++ b/arch/xtensa/include/uapi/asm/mman.h
> > @@ -114,4 +114,8 @@
> >  #define PKEY_ACCESS_MASK     (PKEY_DISABLE_ACCESS |\
> >                                PKEY_DISABLE_WRITE)
> >
> > +/* process_madvise flags */
> > +#define PMADV_FLAG_RANGE     0x1     /* advice for all VMAs in the range */
> > +#define PMADV_FLAG_MASK      (PMADV_FLAG_RANGE)
> > +
> >  #endif /* _XTENSA_MMAN_H */
> > diff --git a/fs/io_uring.c b/fs/io_uring.c
> > index a8c136a1cf4e..508c48b998ee 100644
> > --- a/fs/io_uring.c
> > +++ b/fs/io_uring.c
> > @@ -4118,7 +4118,7 @@ static int io_madvise(struct io_kiocb *req, bool force_nonblock)
> >       if (force_nonblock)
> >               return -EAGAIN;
> >
> > -     ret = do_madvise(current->mm, ma->addr, ma->len, ma->advice);
> > +     ret = do_madvise(current->mm, ma->addr, ma->len, ma->advice, 0);
> >       if (ret < 0)
> >               req_set_fail_links(req);
> >       io_req_complete(req, ret);
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index db6ae4d3fb4e..414c7639e394 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2579,7 +2579,8 @@ extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
> >                      struct list_head *uf, bool downgrade);
> >  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, unsigned long len_in,
> > +                   int behavior, unsigned int flags);
> >
> >  #ifdef CONFIG_MMU
> >  extern int __mm_populate(unsigned long addr, unsigned long len,
> > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> > index f94f65d429be..4898034593ec 100644
> > --- a/include/uapi/asm-generic/mman-common.h
> > +++ b/include/uapi/asm-generic/mman-common.h
> > @@ -80,4 +80,8 @@
> >  #define PKEY_ACCESS_MASK     (PKEY_DISABLE_ACCESS |\
> >                                PKEY_DISABLE_WRITE)
> >
> > +/* process_madvise flags */
> > +#define PMADV_FLAG_RANGE     0x1     /* advice for all VMAs in the range */
> > +#define PMADV_FLAG_MASK      (PMADV_FLAG_RANGE)
> > +
> >  #endif /* __ASM_GENERIC_MMAN_COMMON_H */
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index a8d8d48a57fe..1aa074a46524 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -1001,6 +1001,14 @@ process_madvise_behavior_valid(int behavior)
> >       }
> >  }
> >
> > +static bool can_range_madv_lru_vma(struct vm_area_struct *vma, int behavior)
> > +{
> > +     if (!can_madv_lru_vma(vma))
> > +             return false;
> > +
> > +     return true;
> > +}
> > +
> >  /*
> >   * The madvise(2) system call.
> >   *
> > @@ -1067,15 +1075,21 @@ process_madvise_behavior_valid(int behavior)
> >   *  -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, unsigned long len_in,
> > +            int behavior, unsigned int flags)
> >  {
> >       unsigned long end, tmp;
> >       struct vm_area_struct *vma, *prev;
> >       int unmapped_error = 0;
> >       int error = -EINVAL;
> > +     int error_on_gap;
> >       int write;
> > -     size_t len;
> > +     unsigned long len;
> >       struct blk_plug plug;
> > +     bool range_madvise = !!(flags & PMADV_FLAG_RANGE);
> > +
> > +     /* For range operations gap between VMAs is normal */
> > +     error_on_gap = range_madvise ? 0 : -ENOMEM;
> >
> >       start = untagged_addr(start);
> >
> > @@ -1123,13 +1137,14 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
> >       blk_start_plug(&plug);
> >       for (;;) {
> >               /* Still start < end. */
> > -             error = -ENOMEM;
> > +             error = error_on_gap;
> > +
> >               if (!vma)
> >                       goto out;
> >
> >               /* Here start < (end|vma->vm_end). */
> >               if (start < vma->vm_start) {
> > -                     unmapped_error = -ENOMEM;
> > +                     unmapped_error = error_on_gap;
> >                       start = vma->vm_start;
> >                       if (start >= end)
> >                               goto out;
> > @@ -1140,10 +1155,18 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
> >               if (end < tmp)
> >                       tmp = end;
> >
> > +             /* For range operations skip VMAs ineligible for the behavior */
> > +             if (range_madvise && !can_range_madv_lru_vma(vma, behavior)) {
> > +                     prev = vma;
> > +                     goto skip_vma;
> > +             }
> > +
> >               /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
> >               error = madvise_vma(vma, &prev, start, tmp, behavior);
> >               if (error)
> >                       goto out;
> > +
> > +skip_vma:
> >               start = tmp;
> >               if (prev && start < prev->vm_end)
> >                       start = prev->vm_end;
> > @@ -1167,7 +1190,7 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
> >
> >  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, 0);
> >  }
> >
> >  SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> > @@ -1183,7 +1206,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> >       size_t total_len;
> >       unsigned int f_flags;
> >
> > -     if (flags != 0) {
> > +     if (flags & ~PMADV_FLAG_MASK) {
> >               ret = -EINVAL;
> >               goto out;
> >       }
> > @@ -1216,12 +1239,21 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> >               goto release_task;
> >       }
> >
> > +     /*
> > +      * For range madvise only the entire address space is supported for now
> > +      * and input iovec is ignored.
> > +      */
> > +     if (flags & PMADV_FLAG_RANGE) {
> > +             ret = do_madvise(mm, 0, ULONG_MAX & PAGE_MASK, behavior, flags);
> > +             goto release_mm;
> > +     }
> > +
> >       total_len = iov_iter_count(&iter);
> >
> >       while (iov_iter_count(&iter)) {
> >               iovec = iov_iter_iovec(&iter);
> >               ret = do_madvise(mm, (unsigned long)iovec.iov_base,
> > -                                     iovec.iov_len, behavior);
> > +                                     iovec.iov_len, behavior, flags);
> >               if (ret < 0)
> >                       break;
> >               iov_iter_advance(&iter, iovec.iov_len);
> > @@ -1230,6 +1262,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> >       if (ret == 0)
> >               ret = total_len - iov_iter_count(&iter);
> >
> > +release_mm:
> >       mmput(mm);
> >  release_task:
> >       put_task_struct(task);
> > diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h
> > index f94f65d429be..4898034593ec 100644
> > --- a/tools/include/uapi/asm-generic/mman-common.h
> > +++ b/tools/include/uapi/asm-generic/mman-common.h
> > @@ -80,4 +80,8 @@
> >  #define PKEY_ACCESS_MASK     (PKEY_DISABLE_ACCESS |\
> >                                PKEY_DISABLE_WRITE)
> >
> > +/* process_madvise flags */
> > +#define PMADV_FLAG_RANGE     0x1     /* advice for all VMAs in the range */
> > +#define PMADV_FLAG_MASK      (PMADV_FLAG_RANGE)
> > +
> >  #endif /* __ASM_GENERIC_MMAN_COMMON_H */
> > --
> > 2.29.2.454.gaff20da3a2-goog
> >