Re: [PATCH 00/22] HWPOISON: Intro (v5)

[Wu Fengguang]

On Mon, Jun 15, 2009 at 06:36:19PM +0800, Nick Piggin wrote:
> On Mon, Jun 15, 2009 at 06:09:54PM +0800, Wu Fengguang wrote:
> > On Mon, Jun 15, 2009 at 04:14:53PM +0800, Nick Piggin wrote:
> > > On Mon, Jun 15, 2009 at 08:44:47AM +0200, Nick Piggin wrote:
> > > > Did we verify with filesystem maintainers (eg. btrfs) that the
> > > > !ISREG test will be enough to prevent oopses?
> > > 
> > > BTW. this is quite a significant change I think and not
> > > really documented well enough. Previously a filesystem
> > > will know exactly when and why pagecache in a mapping
> > > under its control will be truncated (as opposed to
> > > invalidated).
> > > 
> > > They even have opportunity to hold locks such as i_mutex.
> > > 
> > > And depending on what they do, they could do interesting
> > > things even with ISREG files.
> > > 
> > > So, I really think this needs review by filesystem
> > > maintainers and it would be far safer to use invalidate
> > > until it is known to be safe.
> > 
> > Nick, we are doing invalidate_complete_page() for !S_ISREG inodes now.
> > Do you mean to do invalidate_complete_page() for all inodes for now?
> 
> That would make me a lot happier. It is obviously correct because
> that is basically what page reclaim and inode reclaim and drop
> caches etc does.
> 
> Note that I still don't like exporting invalidate_complete_page
> fro the same reasons I don't like exporting truncate_complete_page,
> so I will ask if you can do an invalidate_inode_page function
> along the same lines of the truncate_inode_page one please.

Sure. I did something radical - don't try to isolate dirty/writeback
pages, to match the exact invalidate_mapping_pages() behavior.

Let's mess with the dirty/writeback pages some time later.

+/*
+ * Clean (or cleaned) page cache page.
+ */
+static int me_pagecache_clean(struct page *p, unsigned long pfn)
+{
+       struct address_space *mapping;
+
+       if (!isolate_lru_page(p))
+               page_cache_release(p);
+
+       mapping = page_mapping(p);
+       if (mapping == NULL)
+               return RECOVERED;
+
+       /*
+        * Now remove it from page cache.
+        * Currently we only remove clean, unused page for the sake of safety.
+        */
+       if (!invalidate_inode_page(mapping, p)) {
+               printk(KERN_ERR
+                      "MCE %#lx: failed to remove from page cache\n", pfn);
+               return FAILED;
+       }
+       return RECOVERED;
+}


--- sound-2.6.orig/mm/truncate.c
+++ sound-2.6/mm/truncate.c
@@ -135,6 +135,21 @@ invalidate_complete_page(struct address_
        return ret;
 }

+/*
+ * Safely invalidate one page from its pagecache mapping.
+ * It only drops clean, unused pages. The page must be locked.
+ *
+ * Returns 1 if the page is successfully invalidated, otherwise 0.
+ */
+int invalidate_inode_page(struct address_space *mapping, struct page *page)
+{
+       if (PageDirty(page) || PageWriteback(page))
+               return 0;
+       if (page_mapped(page))
+               return 0;
+       return invalidate_complete_page(mapping, page);
+}
+
 /**
  * truncate_inode_pages - truncate range of pages specified by start & end byte offsets
  * @mapping: mapping to truncate
@@ -311,12 +326,8 @@ unsigned long invalidate_mapping_pages(s
                        if (lock_failed)
                                continue;

-                       if (PageDirty(page) || PageWriteback(page))
-                               goto unlock;
-                       if (page_mapped(page))
-                               goto unlock;
-                       ret += invalidate_complete_page(mapping, page);
-unlock:
+                       ret += invalidate_inode_page(mapping, page);
+                       
                        unlock_page(page);
                        if (next > end)
                                break;

> 
> > That's a good suggestion, it shall be able to do the job for most
> > pages indeed.
> 
> Yes I think it will be far far safer while only introducing
> another small class of pages which cannot be recovered (probably
> a much smaller set most of the time than the size of the existing
> set of pages which cannot be recovered).

Anyway, dirty pages are limited to 15% of the total memory by default. 

Thanks,
Fengguang
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