On Fri, Feb 06, 2015 at 04:57:50PM +0100, Michael Kerrisk (man-pages) wrote: > Hi Michael > > On 02/05/2015 04:41 PM, Michal Hocko wrote: > > On Wed 04-02-15 20:24:27, Michael Kerrisk wrote: > > [...] > >> So, how about this text: > >> > >> After a successful MADV_DONTNEED operation, the seman‐ > >> tics of memory access in the specified region are > >> changed: subsequent accesses of pages in the range > >> will succeed, but will result in either reloading of > >> the memory contents from the underlying mapped file > > > > " > > result in either providing the up-to-date contents of the underlying > > mapped file > > " > > Thanks! I did something like that. See below. > > > Would be more precise IMO because reload might be interpreted as a major > > fault which is not necessarily the case (see below). > > > >> (for shared file mappings, shared anonymous mappings, > >> and shmem-based techniques such as System V shared > >> memory segments) or zero-fill-on-demand pages for > >> anonymous private mappings. > > > > Yes, this wording is better because many users are not aware of > > MAP_ANON|MAP_SHARED being file backed in fact and mmap man page doesn't > > mention that. > > (Michal, would you have a text to propose to add to the mmap(2) page? > Maybe it would be useful to add something there.) > > > > > I am just wondering whether it makes sense to mention that MADV_DONTNEED > > for shared mappings might be surprising and not freeing the backing > > pages thus not really freeing memory until there is a memory > > pressure. But maybe this is too implementation specific for a man > > page. What about the following wording on top of yours? > > " > > Please note that the MADV_DONTNEED hint on shared mappings might not > > lead to immediate freeing of pages in the range. The kernel is free to > > delay this until an appropriate moment. RSS of the calling process will > > be reduced however. > > " > > Thanks! I added this, but dropped in the word "immediately" in the last > sentence, since I assume that was implied. So now we have: > > After a successful MADV_DONTNEED operation, the seman‐ > tics of memory access in the specified region are > changed: subsequent accesses of pages in the range will > succeed, but will result in either repopulating the mem‐ > ory contents from the up-to-date contents of the under‐ > lying mapped file (for shared file mappings, shared > anonymous mappings, and shmem-based techniques such as > System V shared memory segments) or zero-fill-on-demand > pages for anonymous private mappings. > > Note that, when applied to shared mappings, MADV_DONT‐ > NEED might not lead to immediate freeing of the pages in > the range. The kernel is free to delay freeing the > pages until an appropriate moment. The resident set > size (RSS) of the calling process will be immediately > reduced however. Looks good. So, I can parse it that anonymous private mappings will lead to immediate freeing of the pages in the range so it's clearly different with MADV_FREE. > > The current draft of the page can be found in a branch, > http://git.kernel.org/cgit/docs/man-pages/man-pages.git/log/?h=draft_madvise > > Thanks, > > Michael > > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
