On Tue, 22 Jul 2014, Jerome Marchand wrote: > Adds get_mm_shswap() which compute the size of swaped out shmem. It > does so by pagewalking the mm and using the new shmem_locate() function > to get the physical location of shmem pages. > The result is displayed in the new VmShSw line of /proc/<pid>/status. > Use mm_walk an shmem_locate() to account paged out shmem pages. > > It significantly slows down /proc/<pid>/status acccess speed when > there is a big shmem mapping. If that is an issue, we can drop this > patch and only display this counter in the inherently slower > /proc/<pid>/smaps file (cf. next patch). > > Signed-off-by: Jerome Marchand <jmarchan@xxxxxxxxxx> Definite NAK to this one. As you guessed yourself, it is always a mistake to add one potentially very slow-to-gather number to a stats file showing a group of quickly gathered numbers. Is there anything you could do instead? I don't know if it's worth the (little) extra mm_struct storage and maintenance, but you could add a VmShmSize, which shows that subset of VmSize (total_vm) which is occupied by shmem mappings. It's ambiguous what to deduce when VmShm is less than VmShmSize: the difference might be swapped out, it might be holes in the sparse object, it might be instantiated in the object but never faulted into the mapping: in general it will be a mix of all of those. So, sometimes useful info, but easy to be misled by it. As I say, I don't know if VmShmSize would be worth adding, given its deficiencies; and it could be worked out from /proc/<pid>/maps anyway. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
