Messages in this thread Patch in this message | | | Date | Thu, 15 Apr 2010 13:01:11 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH] rmap: add exclusively owned pages to the newest anon_vma |
| |
On Wed, 14 Apr 2010, Rik van Riel wrote: > - /* > - * We must use the _oldest_ possible anon_vma for the page mapping! > - * > - * So take the last AVC chain entry in the vma, which is the deepest > - * ancestor, and use the anon_vma from that. > - */ > - avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma); > - anon_vma = avc->anon_vma; > + if (exclusive) > + anon_vma = vma->anon_vma; > + else { > + /* > + * The page may be shared between multiple processes. > + * We must use the _oldest_ possible anon_vma for the > + * page mapping! That anon_vma is guaranteed to be > + * present in all processes that could share this page. > + * > + * So take the last AVC chain entry in the vma, which is the > + * deepest ancestor, and use the anon_vma from that. > + */ > + avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma); > + anon_vma = avc->anon_vma; > + }
I really dislike your coding style.
If we do this conditionally, we're _much_ better off declaring the variables we only use inside that conditional block inside the block itself. And since we access "vma->anon_vma" in either case, just move that case outside the conditional statement, and avoid a pointless if/then/else.
IOW, something like this. Totally untested.
Linus
--- mm/rmap.c | 26 +++++++++++++++----------- 1 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/mm/rmap.c b/mm/rmap.c index 4bad326..78d4730 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -732,21 +732,25 @@ void page_move_anon_rmap(struct page *page, * @address: the user virtual address mapped */ static void __page_set_anon_rmap(struct page *page, - struct vm_area_struct *vma, unsigned long address) + struct vm_area_struct *vma, unsigned long address, int exclusive) { - struct anon_vma_chain *avc; - struct anon_vma *anon_vma; + struct anon_vma *anon_vma = vma->anon_vma; - BUG_ON(!vma->anon_vma); + BUG_ON(!anon_vma); /* - * We must use the _oldest_ possible anon_vma for the page mapping! + * If the page isn't exclusively mapped into this vma, + * we must use the _oldest_ possible anon_vma for the + * page mapping! * - * So take the last AVC chain entry in the vma, which is the deepest - * ancestor, and use the anon_vma from that. + * So take the last AVC chain entry in the vma, which is + * the deepest ancestor, and use the anon_vma from that. */ - avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma); - anon_vma = avc->anon_vma; + if (!exclusive) { + struct anon_vma_chain *avc; + avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma); + anon_vma = avc->anon_vma; + } anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; page->mapping = (struct address_space *) anon_vma; @@ -802,7 +806,7 @@ void page_add_anon_rmap(struct page *page, VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); if (first) - __page_set_anon_rmap(page, vma, address); + __page_set_anon_rmap(page, vma, address, 0); else __page_check_anon_rmap(page, vma, address); } @@ -824,7 +828,7 @@ void page_add_new_anon_rmap(struct page *page, SetPageSwapBacked(page); atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */ __inc_zone_page_state(page, NR_ANON_PAGES); - __page_set_anon_rmap(page, vma, address); + __page_set_anon_rmap(page, vma, address, 1); if (page_evictable(page, vma)) lru_cache_add_lru(page, LRU_ACTIVE_ANON); else
| |