Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756086Ab1FNKoF (ORCPT ); Tue, 14 Jun 2011 06:44:05 -0400 Received: from smtp-out.google.com ([216.239.44.51]:52259 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756062Ab1FNKoB (ORCPT ); Tue, 14 Jun 2011 06:44:01 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=xF/MUsRumagwsINVKSIGeiLY8mmbGiMn5+pyDoI115eothYHXpeIHS24qYD5+xmKCQ NlSvq8Wt+oUHyGQ9M6Tw== Date: Tue, 14 Jun 2011 03:43:47 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Andrew Morton cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 2/12] mm: let swap use exceptional entries In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7523 Lines: 209 If swap entries are to be stored along with struct page pointers in a radix tree, they need to be distinguished as exceptional entries. Most of the handling of swap entries in radix tree will be contained in shmem.c, but a few functions in filemap.c's common code need to check for their appearance: find_get_page(), find_lock_page(), find_get_pages() and find_get_pages_contig(). So as not to slow their fast paths, tuck those checks inside the existing checks for unlikely radix_tree_deref_slot(); except for find_lock_page(), where it is an added test. And make it a BUG in find_get_pages_tag(), which is not applied to tmpfs files. A part of the reason for eliminating shmem_readpage() earlier, was to minimize the places where common code would need to allow for swap entries. The swp_entry_t known to swapfile.c must be massaged into a slightly different form when stored in the radix tree, just as it gets massaged into a pte_t when stored in page tables. In an i386 kernel this limits its information (type and page offset) to 30 bits: given 32 "types" of swapfile and 4kB pagesize, that's a maximum swapfile size of 128GB. Which is less than the 512GB we previously allowed with X86_PAE (where the swap entry can occupy the entire upper 32 bits of a pte_t), but not a new limitation on 32-bit without PAE; and there's not a new limitation on 64-bit (where swap filesize is already limited to 16TB by a 32-bit page offset). Thirty areas of 128GB is probably still enough swap for a 64GB 32-bit machine. Provide swp_to_radix_entry() and radix_to_swp_entry() conversions, and enforce filesize limit in read_swap_header(), just as for ptes. Signed-off-by: Hugh Dickins --- include/linux/swapops.h | 23 +++++++++++++++++ mm/filemap.c | 49 ++++++++++++++++++++++++-------------- mm/swapfile.c | 20 +++++++++------ 3 files changed, 66 insertions(+), 26 deletions(-) --- linux.orig/include/linux/swapops.h 2011-06-13 13:26:07.506101039 -0700 +++ linux/include/linux/swapops.h 2011-06-13 13:27:34.522532530 -0700 @@ -1,3 +1,8 @@ +#ifndef _LINUX_SWAPOPS_H +#define _LINUX_SWAPOPS_H + +#include + /* * swapcache pages are stored in the swapper_space radix tree. We want to * get good packing density in that tree, so the index should be dense in @@ -76,6 +81,22 @@ static inline pte_t swp_entry_to_pte(swp return __swp_entry_to_pte(arch_entry); } +static inline swp_entry_t radix_to_swp_entry(void *arg) +{ + swp_entry_t entry; + + entry.val = (unsigned long)arg >> RADIX_TREE_EXCEPTIONAL_SHIFT; + return entry; +} + +static inline void *swp_to_radix_entry(swp_entry_t entry) +{ + unsigned long value; + + value = entry.val << RADIX_TREE_EXCEPTIONAL_SHIFT; + return (void *)(value | RADIX_TREE_EXCEPTIONAL_ENTRY); +} + #ifdef CONFIG_MIGRATION static inline swp_entry_t make_migration_entry(struct page *page, int write) { @@ -169,3 +190,5 @@ static inline int non_swap_entry(swp_ent return 0; } #endif + +#endif /* _LINUX_SWAPOPS_H */ --- linux.orig/mm/filemap.c 2011-06-13 13:26:44.430284135 -0700 +++ linux/mm/filemap.c 2011-06-13 13:27:34.526532556 -0700 @@ -717,9 +717,12 @@ repeat: page = radix_tree_deref_slot(pagep); if (unlikely(!page)) goto out; - if (radix_tree_deref_retry(page)) + if (radix_tree_exception(page)) { + if (radix_tree_exceptional_entry(page)) + goto out; + /* radix_tree_deref_retry(page) */ goto repeat; - + } if (!page_cache_get_speculative(page)) goto repeat; @@ -756,7 +759,7 @@ struct page *find_lock_page(struct addre repeat: page = find_get_page(mapping, offset); - if (page) { + if (page && !radix_tree_exception(page)) { lock_page(page); /* Has the page been truncated? */ if (unlikely(page->mapping != mapping)) { @@ -852,11 +855,14 @@ repeat: if (unlikely(!page)) continue; - /* - * This can only trigger when the entry at index 0 moves out - * of or back to the root: none yet gotten, safe to restart. - */ - if (radix_tree_deref_retry(page)) { + if (radix_tree_exception(page)) { + if (radix_tree_exceptional_entry(page)) + continue; + /* + * radix_tree_deref_retry(page): + * can only trigger when entry at index 0 moves out of + * or back to root: none yet gotten, safe to restart. + */ WARN_ON(start | i); goto restart; } @@ -915,12 +921,16 @@ repeat: if (unlikely(!page)) continue; - /* - * This can only trigger when the entry at index 0 moves out - * of or back to the root: none yet gotten, safe to restart. - */ - if (radix_tree_deref_retry(page)) + if (radix_tree_exception(page)) { + if (radix_tree_exceptional_entry(page)) + break; + /* + * radix_tree_deref_retry(page): + * can only trigger when entry at index 0 moves out of + * or back to root: none yet gotten, safe to restart. + */ goto restart; + } if (!page_cache_get_speculative(page)) goto repeat; @@ -980,12 +990,15 @@ repeat: if (unlikely(!page)) continue; - /* - * This can only trigger when the entry at index 0 moves out - * of or back to the root: none yet gotten, safe to restart. - */ - if (radix_tree_deref_retry(page)) + if (radix_tree_exception(page)) { + BUG_ON(radix_tree_exceptional_entry(page)); + /* + * radix_tree_deref_retry(page): + * can only trigger when entry at index 0 moves out of + * or back to root: none yet gotten, safe to restart. + */ goto restart; + } if (!page_cache_get_speculative(page)) goto repeat; --- linux.orig/mm/swapfile.c 2011-06-13 13:26:07.506101039 -0700 +++ linux/mm/swapfile.c 2011-06-13 13:27:34.526532556 -0700 @@ -1937,20 +1937,24 @@ static unsigned long read_swap_header(st /* * Find out how many pages are allowed for a single swap - * device. There are two limiting factors: 1) the number of - * bits for the swap offset in the swp_entry_t type and - * 2) the number of bits in the a swap pte as defined by - * the different architectures. In order to find the - * largest possible bit mask a swap entry with swap type 0 + * device. There are three limiting factors: 1) the number + * of bits for the swap offset in the swp_entry_t type, and + * 2) the number of bits in the swap pte as defined by the + * the different architectures, and 3) the number of free bits + * in an exceptional radix_tree entry. In order to find the + * largest possible bit mask, a swap entry with swap type 0 * and swap offset ~0UL is created, encoded to a swap pte, - * decoded to a swp_entry_t again and finally the swap + * decoded to a swp_entry_t again, and finally the swap * offset is extracted. This will mask all the bits from * the initial ~0UL mask that can't be encoded in either * the swp_entry_t or the architecture definition of a - * swap pte. + * swap pte. Then the same is done for a radix_tree entry. */ maxpages = swp_offset(pte_to_swp_entry( - swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1; + swp_entry_to_pte(swp_entry(0, ~0UL)))); + maxpages = swp_offset(radix_to_swp_entry( + swp_to_radix_entry(swp_entry(0, maxpages)))) + 1; + if (maxpages > swap_header->info.last_page) { maxpages = swap_header->info.last_page + 1; /* p->max is an unsigned int: don't overflow it */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/