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Date: Mon, 18 May 2020 12:22:56 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Christian Brauner <christian.brauner@...ntu.com>,
linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
Oleksandr Natalenko <oleksandr@...hat.com>,
Tim Murray <timmurray@...gle.com>,
Daniel Colascione <dancol@...gle.com>,
Sandeep Patil <sspatil@...gle.com>,
Sonny Rao <sonnyrao@...gle.com>,
Brian Geffon <bgeffon@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Johannes Weiner <hannes@...xchg.org>,
Shakeel Butt <shakeelb@...gle.com>,
John Dias <joaodias@...gle.com>,
Joel Fernandes <joel@...lfernandes.org>,
Jann Horn <jannh@...gle.com>,
alexander.h.duyck@...ux.intel.com,
SeongJae Park <sjpark@...zon.com>,
David Rientjes <rientjes@...gle.com>,
Arjun Roy <arjunroy@...gle.com>,
Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [PATCH] mm: use only pidfd for process_madvise syscall
On Fri, May 15, 2020 at 6:21 PM Minchan Kim <minchan@...nel.org> wrote:
>
> Based on discussion[1], people didn't feel we need to support both
> pid and pidfd for every new coming API[2] so this patch keeps only
> pidfd. This patch also changes flags's type with "unsigned int".
> So finally, the API is as follows,
>
> ssize_t process_madvise(int pidfd, const struct iovec *iovec,
> unsigned long vlen, int advice, unsigned int flags);
>
> DESCRIPTION
> The process_madvise() system call is used to give advice or directions
> to the kernel about the address ranges from external process as well as
> local process. It provides the advice to address ranges of process
> described by iovec and vlen. The goal of such advice is to improve system
> or application performance.
>
> The pidfd selects the process referred to by the PID file descriptor
> specified in pidfd. (See pidofd_open(2) for further information)
>
> The pointer iovec points to an array of iovec structures, defined in
> <sys/uio.h> as:
>
> struct iovec {
> void *iov_base; /* starting address */
> size_t iov_len; /* number of bytes to be advised */
> };
>
> The iovec describes address ranges beginning at address(iov_base)
> and with size length of bytes(iov_len).
>
> The vlen represents the number of elements in iovec.
>
> The advice is indicated in the advice argument, which is one of the
> following at this moment if the target process specified by idtype and
There is no idtype parameter anymore, so maybe just "if the target
process is external"?
> id is external.
>
> MADV_COLD
> MADV_PAGEOUT
> MADV_MERGEABLE
> MADV_UNMERGEABLE
>
> Permission to provide a hint to external process is governed by a
> ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
>
> The process_madvise supports every advice madvise(2) has if target
> process is in same thread group with calling process so user could
> use process_madvise(2) to extend existing madvise(2) to support
> vector address ranges.
>
> RETURN VALUE
> On success, process_madvise() returns the number of bytes advised.
> This return value may be less than the total number of requested
> bytes, if an error occurred. The caller should check return value
> to determine whether a partial advice occurred.
>
> [1] https://lore.kernel.org/linux-mm/20200509124817.xmrvsrq3mla6b76k@wittgenstein/
> [2] https://lore.kernel.org/linux-mm/9d849087-3359-c4ab-fbec-859e8186c509@virtuozzo.com/
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> mm/madvise.c | 42 +++++++++++++-----------------------------
> 1 file changed, 13 insertions(+), 29 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index d3fbbe52d230..35c9b220146a 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1229,8 +1229,8 @@ static int process_madvise_vec(struct task_struct *target_task,
> return ret;
> }
>
> -static ssize_t do_process_madvise(int which, pid_t upid, struct iov_iter *iter,
> - int behavior, unsigned long flags)
> +static ssize_t do_process_madvise(int pidfd, struct iov_iter *iter,
> + int behavior, unsigned int flags)
> {
> ssize_t ret;
> struct pid *pid;
> @@ -1241,26 +1241,12 @@ static ssize_t do_process_madvise(int which, pid_t upid, struct iov_iter *iter,
> if (flags != 0)
> return -EINVAL;
>
> - switch (which) {
> - case P_PID:
> - if (upid <= 0)
> - return -EINVAL;
> -
> - pid = find_get_pid(upid);
> - if (!pid)
> - return -ESRCH;
> - break;
> - case P_PIDFD:
> - if (upid < 0)
> - return -EINVAL;
> -
> - pid = pidfd_get_pid(upid);
> - if (IS_ERR(pid))
> - return PTR_ERR(pid);
> - break;
> - default:
> + if (pidfd < 0)
> return -EINVAL;
> - }
> +
> + pid = pidfd_get_pid(pidfd);
> + if (IS_ERR(pid))
> + return PTR_ERR(pid);
>
> task = get_pid_task(pid, PIDTYPE_PID);
> if (!task) {
> @@ -1292,9 +1278,8 @@ static ssize_t do_process_madvise(int which, pid_t upid, struct iov_iter *iter,
> return ret;
> }
>
> -SYSCALL_DEFINE6(process_madvise, int, which, pid_t, upid,
> - const struct iovec __user *, vec, unsigned long, vlen,
> - int, behavior, unsigned long, flags)
> +SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> + unsigned long, vlen, int, behavior, unsigned int, flags)
> {
> ssize_t ret;
> struct iovec iovstack[UIO_FASTIOV];
> @@ -1303,19 +1288,18 @@ SYSCALL_DEFINE6(process_madvise, int, which, pid_t, upid,
>
> ret = import_iovec(READ, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter);
> if (ret >= 0) {
> - ret = do_process_madvise(which, upid, &iter, behavior, flags);
> + ret = do_process_madvise(pidfd, &iter, behavior, flags);
> kfree(iov);
> }
> return ret;
> }
>
> #ifdef CONFIG_COMPAT
> -COMPAT_SYSCALL_DEFINE6(process_madvise, compat_int_t, which,
> - compat_pid_t, upid,
> +COMPAT_SYSCALL_DEFINE5(process_madvise, compat_int_t, pidfd,
> const struct compat_iovec __user *, vec,
> compat_ulong_t, vlen,
> compat_int_t, behavior,
> - compat_ulong_t, flags)
> + compat_int_t, flags)
>
> {
> ssize_t ret;
> @@ -1326,7 +1310,7 @@ COMPAT_SYSCALL_DEFINE6(process_madvise, compat_int_t, which,
> ret = compat_import_iovec(READ, vec, vlen, ARRAY_SIZE(iovstack),
> &iov, &iter);
> if (ret >= 0) {
> - ret = do_process_madvise(which, upid, &iter, behavior, flags);
> + ret = do_process_madvise(pidfd, &iter, behavior, flags);
> kfree(iov);
> }
> return ret;
> --
> 2.26.2.761.g0e0b3e54be-goog
>
Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
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