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NFS: Eliminate nfs_get_user_pages()

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Neil Brown observed that the kmalloc() in nfs_get_user_pages() is more
likely to fail if the I/O is large enough to require the allocation of more
than a single page to keep track of all the pinned pages in the user's
buffer.

Instead of tracking one large page array per dreq/iocb, track pages per
nfs_read/write_data, just like the cached I/O path does.  An array for
pages is already allocated for us by nfs_readdata_alloc() (and the write
and commit equivalents).

This is also required for adding support for vectored I/O to the NFS direct
I/O path.

The original reason to pin the user buffer and allocate all the NFS data
structures before trying to schedule I/O was to ensure all needed resources
are allocated on the client before starting to send requests.  This reduces
the chance that resource exhaustion on the client will cause a short read
or write.

On the other hand, for an application making very large application I/O
requests, this means that it will be nearly impossible for the application
to make forward progress on a resource-limited client.

Thus, moving the buffer pinning functionality into the I/O scheduling
loops should be good for scalability.  The next patch will do the same for
NFS data structure allocation.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Chuck Lever
2006-06-20 12:56:49 -04:00
committed by Trond Myklebust
parent 9c93ab7dff
commit 06cf6f2ed0
2 changed files with 113 additions and 94 deletions
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2
include/linux/nfs_xdr.h
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@@ -729,6 +729,7 @@ struct nfs_read_data {
struct list_head pages; /* Coalesced read requests */
struct nfs_page *req; /* multi ops per nfs_page */
struct page **pagevec;
unsigned int npages; /* active pages in pagevec */
struct nfs_readargs args;
struct nfs_readres res;
#ifdef CONFIG_NFS_V4
@@ -747,6 +748,7 @@ struct nfs_write_data {
struct list_head pages; /* Coalesced requests we wish to flush */
struct nfs_page *req; /* multi ops per nfs_page */
struct page **pagevec;
unsigned int npages; /* active pages in pagevec */
struct nfs_writeargs args; /* argument struct */
struct nfs_writeres res; /* result struct */
#ifdef CONFIG_NFS_V4