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cifs: on CONFIG_HIGHMEM machines, limit the rsize/wsize to the kmap space

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We currently rely on being able to kmap all of the pages in an async
read or write request. If you're on a machine that has CONFIG_HIGHMEM
set then that kmap space is limited, sometimes to as low as 512 slots.

With 512 slots, we can only support up to a 2M r/wsize, and that's
assuming that we can get our greedy little hands on all of them. There
are other users however, so it's possible we'll end up stuck with a
size that large.

Since we can't handle a rsize or wsize larger than that currently, cap
those options at the number of kmap slots we have. We could consider
capping it even lower, but we currently default to a max of 1M. Might as
well allow those luddites on 32 bit arches enough rope to hang
themselves.

A more robust fix would be to teach the send and receive routines how
to contend with an array of pages so we don't need to marshal up a kvec
array at all. That's a fairly significant overhaul though, so we'll need
this limit in place until that's ready.

Cc: <stable@vger.kernel.org>
Reported-by: Jian Li <jiali@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
This commit is contained in:
Jeff Layton 2012-07-11 09:09:35 -04:00 committed by Steve French
parent ffc61ccbb9
commit 3ae629d98b
1 changed files with 18 additions and 0 deletions
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18
fs/cifs/connect.c
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@ -3445,6 +3445,18 @@ void cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
#define CIFS_DEFAULT_NON_POSIX_RSIZE (60 * 1024)
#define CIFS_DEFAULT_NON_POSIX_WSIZE (65536)
/*
* On hosts with high memory, we can't currently support wsize/rsize that are
* larger than we can kmap at once. Cap the rsize/wsize at
* LAST_PKMAP * PAGE_SIZE. We'll never be able to fill a read or write request
* larger than that anyway.
*/
#ifdef CONFIG_HIGHMEM
#define CIFS_KMAP_SIZE_LIMIT (LAST_PKMAP * PAGE_CACHE_SIZE)
#else /* CONFIG_HIGHMEM */
#define CIFS_KMAP_SIZE_LIMIT (1<<24)
#endif /* CONFIG_HIGHMEM */
static unsigned int
cifs_negotiate_wsize(struct cifs_tcon *tcon, struct smb_vol *pvolume_info)
{
@ -3475,6 +3487,9 @@ cifs_negotiate_wsize(struct cifs_tcon *tcon, struct smb_vol *pvolume_info)
wsize = min_t(unsigned int, wsize,
server->maxBuf - sizeof(WRITE_REQ) + 4);
/* limit to the amount that we can kmap at once */
wsize = min_t(unsigned int, wsize, CIFS_KMAP_SIZE_LIMIT);
/* hard limit of CIFS_MAX_WSIZE */
wsize = min_t(unsigned int, wsize, CIFS_MAX_WSIZE);
@ -3516,6 +3531,9 @@ cifs_negotiate_rsize(struct cifs_tcon *tcon, struct smb_vol *pvolume_info)
if (!(server->capabilities & CAP_LARGE_READ_X))
rsize = min_t(unsigned int, CIFSMaxBufSize, rsize);
/* limit to the amount that we can kmap at once */
rsize = min_t(unsigned int, rsize, CIFS_KMAP_SIZE_LIMIT);
/* hard limit of CIFS_MAX_RSIZE */
rsize = min_t(unsigned int, rsize, CIFS_MAX_RSIZE);