path: root/mm
diff options
authorNick Piggin <>2009-01-06 14:40:28 -0800
committerLinus Torvalds <>2009-01-06 15:59:09 -0800
commit67d58ac47d25f7e2a105248a4aea6113131ab874 (patch)
tree5bf9440696b72ec0962d352c6d60b81929b79602 /mm
parent856bf4d717feb8c55d4e2f817b71ebb70cfbc67b (diff)
mm: pagecache gfp flags fix
Frustratingly, gfp_t is really divided into two classes of flags. One are the context dependent ones (can we sleep? can we enter filesystem? block subsystem? should we use some extra reserves, etc.). The other ones are the type of memory required and depend on how the algorithm is implemented rather than the point at which the memory is allocated (highmem? dma memory? etc). Some of the functions which allocate a page and add it to page cache take a gfp_t, but sometimes those functions or their callers aren't really doing the right thing: when allocating pagecache page, the memory type should be mapping_gfp_mask(mapping). When allocating radix tree nodes, the memory type should be kernel mapped (not highmem) memory. The gfp_t argument should only really be needed for context dependent options. This patch doesn't really solve that tangle in a nice way, but it does attempt to fix a couple of bugs. - find_or_create_page changes its radix-tree allocation to only include the main context dependent flags in order so the pagecache page may be allocated from arbitrary types of memory without affecting the radix-tree. In practice, slab allocations don't come from highmem anyway, and radix-tree only uses slab allocations. So there isn't a practical change (unless some fs uses GFP_DMA for pages). - grab_cache_page_nowait() is changed to allocate radix-tree nodes with GFP_NOFS, because it is not supposed to reenter the filesystem. This bug could cause lock recursion if a filesystem is not expecting the function to reenter the fs (as-per documentation). Filesystems should be careful about exactly what semantics they want and what they get when fiddling with gfp_t masks to allocate pagecache. One should be as liberal as possible with the type of memory that can be used, and same for the the context specific flags. Signed-off-by: Nick Piggin <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm')
1 files changed, 9 insertions, 2 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index f3555fb806d..2f55a1e2baf 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -741,7 +741,14 @@ repeat:
page = __page_cache_alloc(gfp_mask);
if (!page)
return NULL;
- err = add_to_page_cache_lru(page, mapping, index, gfp_mask);
+ /*
+ * We want a regular kernel memory (not highmem or DMA etc)
+ * allocation for the radix tree nodes, but we need to honour
+ * the context-specific requirements the caller has asked for.
+ * GFP_RECLAIM_MASK collects those requirements.
+ */
+ err = add_to_page_cache_lru(page, mapping, index,
+ (gfp_mask & GFP_RECLAIM_MASK));
if (unlikely(err)) {
page = NULL;
@@ -950,7 +957,7 @@ grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
return NULL;
page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
- if (page && add_to_page_cache_lru(page, mapping, index, GFP_KERNEL)) {
+ if (page && add_to_page_cache_lru(page, mapping, index, GFP_NOFS)) {
page = NULL;