On Fri, 2 Oct 2015 15:35:49 +0200 Vlastimil Babka <vbabka@xxxxxxx> 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. > > ... > > --- a/include/linux/shmem_fs.h > +++ b/include/linux/shmem_fs.h > @@ -60,6 +60,12 @@ extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping, > extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end); > extern int shmem_unuse(swp_entry_t entry, struct page *page); > > +#ifdef CONFIG_SWAP > +extern unsigned long shmem_swap_usage(struct inode *inode); > +extern unsigned long shmem_partial_swap_usage(struct address_space *mapping, > + pgoff_t start, pgoff_t end); > +#endif CONFIG_SWAP is wrong, isn't it? It should be CONFIG_SHMEM if anything. I'd just do --- a/include/linux/shmem_fs.h~mm-proc-account-for-shmem-swap-in-proc-pid-smaps-fix +++ a/include/linux/shmem_fs.h @@ -60,11 +60,9 @@ extern struct page *shmem_read_mapping_p extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end); extern int shmem_unuse(swp_entry_t entry, struct page *page); -#ifdef CONFIG_SWAP extern unsigned long shmem_swap_usage(struct inode *inode); extern unsigned long shmem_partial_swap_usage(struct address_space *mapping, pgoff_t start, pgoff_t end); -#endif static inline struct page *shmem_read_mapping_page( struct address_space *mapping, pgoff_t index) We don't need the ifdefs around declarations and they're a pain to maintain and they'd add a *ton* of clutter if we even tried to do this for real. -- 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
