From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f50.google.com (mail-oi0-f50.google.com [209.85.218.50]) by kanga.kvack.org (Postfix) with ESMTP id C376B6B0032 for ; Fri, 27 Feb 2015 05:38:25 -0500 (EST) Received: by mail-oi0-f50.google.com with SMTP id v1so14876398oia.9 for ; Fri, 27 Feb 2015 02:38:25 -0800 (PST) Received: from mail-oi0-x233.google.com (mail-oi0-x233.google.com. [2607:f8b0:4003:c06::233]) by mx.google.com with ESMTPS id 184si1172265oig.46.2015.02.27.02.38.25 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 27 Feb 2015 02:38:25 -0800 (PST) Received: by mail-oi0-f51.google.com with SMTP id g201so14845556oib.10 for ; Fri, 27 Feb 2015 02:38:25 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1424958666-18241-3-git-send-email-vbabka@suse.cz> References: <1424958666-18241-1-git-send-email-vbabka@suse.cz> <1424958666-18241-3-git-send-email-vbabka@suse.cz> From: Michael Kerrisk Date: Fri, 27 Feb 2015 11:38:04 +0100 Message-ID: Subject: Re: [PATCH 2/4] mm, procfs: account for shmem swap in /proc/pid/smaps Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: linux-mm , Jerome Marchand , Linux Kernel , Andrew Morton , linux-doc , Hugh Dickins , Michal Hocko , "Kirill A. Shutemov" , Cyrill Gorcunov , Randy Dunlap , linux-s390 , Martin Schwidefsky , Heiko Carstens , Peter Zijlstra , Paul Mackerras , Arnaldo Carvalho de Melo , Oleg Nesterov , Linux API [CC += linux-api@] On Thu, Feb 26, 2015 at 2:51 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. > > Signed-off-by: Vlastimil Babka > --- > Documentation/filesystems/proc.txt | 3 ++- > fs/proc/task_mmu.c | 20 ++++++++++++++++++++ > 2 files changed, 22 insertions(+), 1 deletion(-) > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > index d4f56ec..8b30543 100644 > --- a/Documentation/filesystems/proc.txt > +++ b/Documentation/filesystems/proc.txt > @@ -437,7 +437,8 @@ indicates the amount of memory currently marked as referenced or accessed. > a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE > and a page is modified, the file page is replaced by a private anonymous copy. > "Swap" shows how much would-be-anonymous memory is also used, but out on > -swap. > +swap. For shmem mappings, "Swap" shows how much of the mapped portion of the > +underlying shmem object is on swap. > > "VmFlags" field deserves a separate description. This member represents the kernel > flags associated with the particular virtual memory area in two letter encoded > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 956b75d..0410309 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -13,6 +13,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -496,6 +497,25 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr, > mss->swap += PAGE_SIZE; > else if (is_migration_entry(swpent)) > page = migration_entry_to_page(swpent); > + } else if (IS_ENABLED(CONFIG_SHMEM) && IS_ENABLED(CONFIG_SWAP) && > + pte_none(*pte) && vma->vm_file) { > + struct address_space *mapping = > + file_inode(vma->vm_file)->i_mapping; > + > + /* > + * shmem does not use swap pte's so we have to consult > + * the radix tree to account for swap > + */ > + if (shmem_mapping(mapping)) { > + page = find_get_entry(mapping, pgoff); > + if (page) { > + if (radix_tree_exceptional_entry(page)) > + mss->swap += PAGE_SIZE; > + else > + page_cache_release(page); > + } > + page = NULL; > + } > } > > if (!page) > -- > 2.1.4 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface", http://blog.man7.org/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org