Hi Michael, On Tue, Feb 2, 2021 at 2:45 AM Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > > Hello Suren (and Minchan and Michal) > > Thank you for the revisions! > > I've applied this patch, and done a few light edits. Thanks! > > However, I have a questions about undocumented pieces in *madvise(2)*, > as well as one other question. See below. > > On 2/2/21 6:30 AM, Suren Baghdasaryan wrote: > > Initial version of process_madvise(2) manual page. Initial text was > > extracted from [1], amended after fix [2] and more details added using > > man pages of madvise(2) and process_vm_read(2) as examples. It also > > includes the changes to required permission proposed in [3]. > > > > [1] https://lore.kernel.org/patchwork/patch/1297933/ > > [2] https://lkml.org/lkml/2020/12/8/1282 > > [3] https://patchwork.kernel.org/project/selinux/patch/20210111170622.2613577-1-surenb@xxxxxxxxxx/#23888311 > > > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > Reviewed-by: Michal Hocko <mhocko@xxxxxxxx> > > --- > > changes in v2: > > - Changed description of MADV_COLD per Michal Hocko's suggestion > > - Applied fixes suggested by Michael Kerrisk > > changes in v3: > > - Added Michal's Reviewed-by > > - Applied additional fixes suggested by Michael Kerrisk > > > > NAME > > process_madvise - give advice about use of memory to a process > > > > SYNOPSIS > > #include <sys/uio.h> > > > > 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 of another process or the calling > > process. It provides the advice to the address ranges described by iovec > > and vlen. The goal of such advice is to improve system or application > > performance. > > > > The pidfd argument is a PID file descriptor (see pidfd_open(2)) that > > specifies the process to which the advice is to be applied. > > > > 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 transfer */ > > }; > > > > The iovec structure describes address ranges beginning at iov_base address > > and with the size of iov_len bytes. > > > > The vlen represents the number of elements in the iovec structure. > > > > The advice argument is one of the values listed below. > > > > Linux-specific advice values > > The following Linux-specific advice values have no counterparts in the > > POSIX-specified posix_madvise(3), and may or may not have counterparts > > in the madvise(2) interface available on other implementations. > > > > MADV_COLD (since Linux 5.4.1) > > I just noticed these version numbers now, and thought: they can't be > right (because the system call appeared only in v5.11). So I removed > them. But, of course in another sense the version numbers are (nearly) > right, since these advice values were added for madvise(2) in Linux 5.4. > However, they are not documented in the madvise(2) manual page. Is it > correct to assume that MADV_COLD and MADV_PAGEOUT have exactly the same > meaning in madvise(2) (but just for the calling process, of course)? Correct. They should be added in the madvise(2) man page as well IMHO. > > > Deactive a given range of pages which will make them a more probable > > I changed: s/Deactive/Deactivate/ thanks! > > > reclaim target should there be a memory pressure. This is a > > nondestructive operation. The advice might be ignored for some pages > > in the range when it is not applicable. > > > > MADV_PAGEOUT (since Linux 5.4.1) > > Reclaim a given range of pages. This is done to free up memory occupied > > by these pages. If a page is anonymous it will be swapped out. If a > > page is file-backed and dirty it will be written back to the backing > > storage. The advice might be ignored for some pages in the range when > > it is not applicable. > > [...] > > > The hint might be applied to a part of iovec if one of its elements points > > to an invalid memory region in the remote process. No further elements will > > be processed beyond that point. > > Is the above scenario the one that leads to the partial advice case described in > RETURN VALUE? If yes, perhaps I should add some words to make that clearer. Correct. This describes the case when partial advice happens. > > You can see the light edits that I made in > https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=e3ce016472a1b3ec5dffdeb23c98b9fef618a97b > and following that I restructured DESCRIPTION a little in > https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=3aac0708a9acee5283e091461de6a8410bc921a6 The edits LGTM. Thanks, Suren. > > Thanks, > > Michael > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/
