On Mon, 2007-10-15 at 18:11 -0500, Matt Mackall wrote: > > Could we just have /proc/kpagereferenced? Is there a legitimate need > > for other flags to be visible? > > Referenced, dirty, uptodate, lru, active, slab, writeback, reclaim, > and buddy all look like they might be interesting to me from the point > of view of watching what's happening in the VM graphically in > real-time.
This is true, but it forces a lot of logic from the kernel to be run in userspace to figure out what is going on. Looking at mainline today: #define PG_reclaim 17 /* To be reclaimed asap */ ... #define PG_readahead PG_reclaim /* Reminder to do async read-ahead */ All of a sudden, to figure out which flag it actually is, we need to have all of the logic that the kernel does. Does this establish a fixed user<->kernel ABI that will keep us from doing this in the future: -#define PG_slab 7 /* slab debug (Suparna wants this) */ +#define PG_slab 14 /* slab debug (Suparna wants this) */ Or, even something like this: -#define PageSlab(page) test_bit(PG_slab, &(page)->flags) +#define PageSlab(page) (!PageLRU(page) && !PageHighmem(page)) If we actually had several (or even still one file) that exposed this state, independent of the actual content of page->flags, I think we'd be better off. I think that's the difference between a fun, super-useful debugging feature and one that can stay in mainline and have applications stay using it (without breaking) for a long time. The flags you listed are things that I would imagine will always exist, logically. But, we might not always have a specific page flag for pages under writeback or in the buddy list for that matter. PG_buddy isn't that old. Perhaps that would be better abstracted to something like page_in_main_allocator(). -- Dave - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/