Hi. The new address_space_ops is_partially_uptodate was added at 2.6.27-rc1. On ext3, this aops checks whether buffer_heads that are attached to a page are uptodate or not when a page is not uptodate. When all buffers which correspond to a portion we want to read are uptodate even if a page is not uptodate, we can avoid actual read IO. See http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=8ab22b9abb5c55413802e4adc9aa6223324547c3;hp=d84a52f62f6a396ed77aa0052da74ca9e760b28a I wrote is_partially_uptodate aops for nfs named nfs_is_partially_uptodate.This aops checks whether read IO to a page is between wb_pgbase and wb_pgbase + wb_bytes of nfs_page that is attached to this page. If this aops succeed, we do not have to do actual read. I think random read/write mixed workloads or random read after random write workloads can be optimized with this patch. Thanks. Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> diff -Nrup linux-2.6.27-rc5.org/fs/nfs/file.c linux-2.6.27-rc5.nfs/fs/nfs/file.c --- linux-2.6.27-rc5.org/fs/nfs/file.c 2008-09-03 14:56:16.000000000 +0900 +++ linux-2.6.27-rc5.nfs/fs/nfs/file.c 2008-09-08 10:53:00.000000000 +0900 @@ -446,6 +446,7 @@ const struct address_space_operations nf .releasepage = nfs_release_page, .direct_IO = nfs_direct_IO, .launder_page = nfs_launder_page, + .is_partially_uptodate = nfs_is_partially_uptodate, }; static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page) diff -Nrup linux-2.6.27-rc5.org/fs/nfs/read.c linux-2.6.27-rc5.nfs/fs/nfs/read.c --- linux-2.6.27-rc5.org/fs/nfs/read.c 2008-07-14 06:51:29.000000000 +0900 +++ linux-2.6.27-rc5.nfs/fs/nfs/read.c 2008-09-08 11:02:59.000000000 +0900 @@ -605,6 +605,33 @@ out: return ret; } +int nfs_is_partially_uptodate(struct page *page, read_descriptor_t *desc, + unsigned long from) +{ + struct inode *inode = page->mapping->host; + unsigned to; + struct nfs_page *req = NULL; + + spin_lock(&inode->i_lock); + if (PagePrivate(page)) { + req = (struct nfs_page *)page_private(page); + if (req) + kref_get(&req->wb_kref); + } + spin_unlock(&inode->i_lock); + if (!req) + return 0; + + to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count); + to = from + to; + if (from >= req->wb_pgbase && to <= req->wb_pgbase + req->wb_bytes) { + nfs_release_request(req); + return 1; + } + nfs_release_request(req); + return 0; +} + int __init nfs_init_readpagecache(void) { nfs_rdata_cachep = kmem_cache_create("nfs_read_data", diff -Nrup linux-2.6.27-rc5.org/include/linux/nfs_fs.h linux-2.6.27-rc5.nfs/include/linux/nfs_fs.h --- linux-2.6.27-rc5.org/include/linux/nfs_fs.h 2008-09-03 14:56:20.000000000 +0900 +++ linux-2.6.27-rc5.nfs/include/linux/nfs_fs.h 2008-09-08 11:04:28.000000000 +0900 @@ -504,6 +504,8 @@ extern int nfs_readpages(struct file *, struct list_head *, unsigned); extern int nfs_readpage_result(struct rpc_task *, struct nfs_read_data *); extern void nfs_readdata_release(void *data); +extern int nfs_is_partially_uptodate(struct page *, read_descriptor_t *, + unsigned long); /* * Allocate nfs_read_data structures -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
