Hi Michael, On Sat, Feb 13, 2021 at 2:04 PM Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > > Hello Suren, > > On 2/2/21 11:12 PM, Suren Baghdasaryan wrote: > > 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. > > So, I decided to move the description of MADV_COLD and MADV_PAGEOUT > to madvise(2) and refer to that page from the process_madvise(2) > page. This avoids repeating the same information in two places. Sounds good. > > >>> 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. > > Thanks. I added a few words to clarify this. Any link where I can see the final version? > > > >> 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 for checking them. > > Cheers, > > Michael > Thanks, Suren. > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. >
