On 10/02/2015 03:35 PM, Vlastimil Babka wrote: > Currently, /proc/pid/smaps will always show "Swap: 0 kB" for shmem-backed > mappings, even if the mapped portion does contain pages that were swapped out. > This is because unlike private anonymous mappings, shmem does not change pte > to swap entry, but pte_none when swapping the page out. In the smaps page > walk, such page thus looks like it was never faulted in. > > This patch changes smaps_pte_entry() to determine the swap status for such > pte_none entries for shmem mappings, similarly to how mincore_page() does it. > Swapped out pages are thus accounted for. > > The accounting is arguably still not as precise as for private anonymous > mappings, since now we will count also pages that the process in question never > accessed, but only another process populated them and then let them become > swapped out. I believe it is still less confusing and subtle than not showing > any swap usage by shmem mappings at all. Also, swapped out pages only becomee a > performance issue for future accesses, and we cannot predict those for neither > kind of mapping. Agreed, this is much better than the current situation. I don't think there is such a thing as a perfect accounting of shared pages anyway. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
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