On Tue, 6 Jan 2015, Andrew Morton wrote: > On Tue, 6 Jan 2015 17:04:33 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > On Tue, 6 Jan 2015, Andrew Morton wrote: > > > On Fri, 26 Dec 2014 19:56:49 +0800 "Wang, Yalin" <Yalin.Wang@xxxxxxxxxxxxxx> wrote: > > > > > > > This patch subtract sharedram from cached, > > > > sharedram can only be swap into swap partitions, > > > > they should be treated as swap pages, not as cached pages. > > > > > > > > ... > > > > > > > > --- a/fs/proc/meminfo.c > > > > +++ b/fs/proc/meminfo.c > > > > @@ -45,7 +45,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v) > > > > committed = percpu_counter_read_positive(&vm_committed_as); > > > > > > > > cached = global_page_state(NR_FILE_PAGES) - > > > > - total_swapcache_pages() - i.bufferram; > > > > + total_swapcache_pages() - i.bufferram - i.sharedram; > > > > if (cached < 0) > > > > cached = 0; > > > > > > Documentation/filesystems/proc.txt says > > > > > > : Cached: in-memory cache for files read from the disk (the > > > : pagecache). Doesn't include SwapCached > > > > > > So yes, I guess it should not include shmem. > > > > > > And why not do this as well? > > > > > > > > > --- a/Documentation/filesystems/proc.txt~mm-change-meminfo-cached-calculation-fix > > > +++ a/Documentation/filesystems/proc.txt > > > @@ -811,7 +811,7 @@ MemAvailable: An estimate of how much me > > > Buffers: Relatively temporary storage for raw disk blocks > > > shouldn't get tremendously large (20MB or so) > > > Cached: in-memory cache for files read from the disk (the > > > - pagecache). Doesn't include SwapCached > > > + pagecache). Doesn't include SwapCached or Shmem. > > > SwapCached: Memory that once was swapped out, is swapped back in but > > > still also is in the swapfile (if memory is needed it > > > doesn't need to be swapped out AGAIN because it is already > > > > Whoa. Changes of this kind would have made good sense about 14 years ago. > > And there's plenty more which would benefit from having anon/shmem/file > > properly distinguished. But how can we make such a change now, > > breaking everything that has made its own sense of these counts? > > That's what I was wondering, but I was having some trouble picking a > situation where it mattered much. If it doesn't matter, then we don't need to change it. > What's the problematic scenario > here? Userspace that is taking Cached, saying "that was silly" and > subtracting Shmem from it by hand? Someone a long time ago saw "that was silly", worked out it was because of Shmem, adjusted their scripts or whatever accordingly, and has run happily ever since. > > I suppose that as nobody knows we should err on the side of caution and > leave this alone. But the situation is pretty sad - it would be nice > to make the code agree with the documentation at least. By all means fix the documentation. And work on a /proc/meminfo.2015 which has sensibly differentiated counts (and probably omits that wonderful Linux 2.2-compatible "Buffers"). But there's more to do than I can think of. Cc'ing Jerome who has a particular interest in this (no, I haven't forgotten his patches, but nor have I had a moment to reconsider them). Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>