Messages in this thread | | | Date | Wed, 11 Mar 2009 17:02:07 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache may get wrongly discarded |
| |
On Wed, 11 Mar 2009 15:03:02 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> > The problem is that the pages are not marked dirty. Anything that creates data > > in an MMU-based ramfs will cause the pages holding that data will cause the > > set_page_dirty() aop to be called. > > > > For the NOMMU-based mmap, set_page_dirty() may be called by write(), but it > > won't be called by page-writing faults on writable mmaps, and it isn't called > > by ramfs_nommu_expand_for_mapping() when a file is being truncated from nothing > > to allocate a contiguous run. > > > > The solution is to mark the pages dirty at the point of allocation by > > the truncation code. > > Page reclaim shouldn't be even attempting to reclaim or write back > ramfs pagecache pages - reclaim can't possibly do anything with these > pages! > > Arguably those pages shouldn't be on the LRU at all, but we haven't > done that yet. > > Now, my problem is that I can't 100% be sure that we _ever_ implemented > this properly. I _think_ we did, in which case we later broke it. If > we've always been (stupidly) trying to pageout these pages then OK, I > guess your patch is a suitable 2.6.29 stopgap.
OK, I can't find any code anywhere in which we excluded ramfs pages from consideration by page reclaim. How dumb.
So I guess that for now the proposed patch is suitable. Longer-term we should bale early in shrink_page_list(), or not add these pages to the LRU at all.
| |