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Date: Sat, 26 Jan 2008 22:03:51 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Shaohua Li <shaohua.li@...el.com> Cc: nickpiggin@...oo.com.au, clameter@....com, linux-kernel@...r.kernel.org Subject: Re: [RFC] some page can't be migrated > On Fri, 25 Jan 2008 14:03:25 +0800 Shaohua Li <shaohua.li@...el.com> wrote: > > - if (!page->mapping) > + if (!page->mapping) { > + if (!PageAnon(page) && PagePrivate(page)) > + try_to_release_page(page, GFP_KERNEL); > goto rcu_unlock; > + } We call something(GFP_KERNEL) under rcu_read_lock()? I've lost track of the myriad flavours of rcu which we purport to support, but I don't think they'll all like us blocking under rcu_read_lock(). We _won't_ block, because try_to_release_page() will see the NULL ->mapping and will call the non-blocking try_to_free_buffers(). But still, it looks bad, and will cause problems if someone decides to add a might_sleep_if() to try_to_release_page(). So... I'd suggest that it would be better to add an apologetic comment and call direct into try_to_free_buffers(). > - * This is a corner case handling. > - * When a new swap-cache is read into, it is linked to LRU > + * There are corner cases handling. > + * 1. When a new swap-cache is read into, it is linked to LRU hm, that didn't improve the rather flakey grammar in there. Oh well. > Acked-by: Nick Piggin <npiggin@...e.de> > Acked-by: Christoph Lameter <clameter@....com> hm. Please review and test.... --- a/mm/migrate.c~page-migraton-handle-orphaned-pages-fix +++ a/mm/migrate.c @@ -650,20 +650,28 @@ static int unmap_and_move(new_page_t get } /* - * There are corner cases handling. - * 1. When a new swap-cache is read into, it is linked to LRU - * and treated as swapcache but has no rmap yet. - * Calling try_to_unmap() against a page->mapping==NULL page is - * BUG. So handle it here. - * 2. Orphaned page (see truncate_complete_page) might have - * fs-private metadata, the page is truncated. The page can be picked - * up due to memory offlineing. Everywhere else except page reclaim, - * the page is invisible to the vm, so the page can't be migrated. Try - * to free metadata, so the page can be freed. + * Corner case handling: + * 1. When a new swap-cache page is read into, it is added to the LRU + * and treated as swapcache but it has no rmap yet. + * Calling try_to_unmap() against a page->mapping==NULL page will + * trigger a BUG. So handle it here. + * 2. An orphaned page (see truncate_complete_page) might have + * fs-private metadata. The page can be picked up due to memory + * offlining. Everywhere else except page reclaim, the page is + * invisible to the vm, so the page can not be migrated. So try to + * free the metadata, so the page can be freed. */ if (!page->mapping) { - if (!PageAnon(page) && PagePrivate(page)) - try_to_release_page(page, GFP_KERNEL); + if (!PageAnon(page) && PagePrivate(page)) { + /* + * Go direct to try_to_free_buffers() here because + * a) that's what try_to_release_page() would do anyway + * b) we may be under rcu_read_lock() here, so we can't + * use GFP_KERNEL which is what try_to_release_page() + * needs to be effective. + */ + try_to_release_buffers(page); + } goto rcu_unlock; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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