On Thu, 2008-11-27 at 11:18 +0100, Nick Piggin wrote: > On Thu, Nov 27, 2008 at 11:52:40AM +0200, Pekka Enberg wrote: > > > - err = add_to_page_cache_lru(page, mapping, index, gfp_mask); > > > + err = add_to_page_cache_lru(page, mapping, index, > > > + (gfp_mask & (__GFP_FS|__GFP_IO|__GFP_WAIT|__GFP_HIGH))); > > > > Can we use GFP_RECLAIM_MASK here? I mean, surely we need to pass > > __GFP_NOFAIL, for example, down to radix_tree_preload() et al? > > Updated patch. > > -- > 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 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. Then grab_cache_page_nowait() is changed to allocate radix-tree > nodes with GFP_NOFS, because it is not supposed to reenter the filesystem. > > 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 <npiggin@xxxxxxx> Looks good to me. Reviewed-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > --- > Index: linux-2.6/mm/filemap.c > =================================================================== > --- linux-2.6.orig/mm/filemap.c > +++ linux-2.6/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_cache_release(page); > page = NULL; > @@ -950,7 +957,7 @@ grab_cache_page_nowait(struct address_sp > 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_cache_release(page); > page = NULL; > } -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html