On 11/18/2010 12:09 AM, Jeff Layton wrote:
> On Wed, 17 Nov 2010 23:53:34 +0530
> Suresh Jayaraman <sjayaraman@xxxxxxx> wrote:
>
>> Currently, the attribute cache timeout for CIFS is hardcoded to 1 second. This
>> means that the client might have to issue a QPATHINFO/QFILEINFO call every 1
>> second to verify if something has changes, which seems too expensive. On the
>> other hand, if the timeout is hardcoded to a higher value, workloads that
>> expect strict cache coherency might see unexpected results.
>>
>> Making attribute cache timeout as a tunable will allow us to make a tradeoff
>> between performance and cache metadata correctness depending on the
>> application/workload needs.
>>
>> Add 'actimeo' tunable that can be used to tune the attribute cache timeout.
>> The default timeout is set to 1 second.
>>
>> Also, display actimeo option value in /proc/mounts.
>>
>> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
>> Signed-off-by: Suresh Jayaraman <sjayaraman@xxxxxxx>
>> ---
>> fs/cifs/cifs_fs_sb.h | 1 +
>> fs/cifs/cifsfs.c | 1 +
>> fs/cifs/cifsglob.h | 5 +++++
>> fs/cifs/connect.c | 10 ++++++++++
>> fs/cifs/inode.c | 6 +++---
>> 5 files changed, 20 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
>> index ff7d299..f30700d 100644
>> --- a/fs/cifs/inode.c
>> +++ b/fs/cifs/inode.c
>> @@ -1648,6 +1648,7 @@ static bool
>> cifs_inode_needs_reval(struct inode *inode)
>> {
>> struct cifsInodeInfo *cifs_i = CIFS_I(inode);
>> + struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
>>
>> if (cifs_i->clientCanCacheRead)
>> return false;
>> @@ -1658,12 +1659,11 @@ cifs_inode_needs_reval(struct inode *inode)
>> if (cifs_i->time == 0)
>> return true;
>>
>> - /* FIXME: the actimeo should be tunable */
>> - if (time_after_eq(jiffies, cifs_i->time + HZ))
>> + if (time_after_eq(jiffies, cifs_i->time + (cifs_sb->actimeo * HZ)))
>
> Problem:
>
> Suppose (cifs_i->time + (cifs_sb->actimeo * HZ)) carries you
> past two sign bit changes. At that point, it may look like
> the resulting time is in the past, not the future.
Good catch.
> You actually do need to impose a limit here. I suggest looking
> very closely at time_before/time_after macros. It'll also be
> easier to deal storing actimeo in terms of jiffies instead of
> seconds.
> Finally, this value needs to be displayed in /proc/mounts.
>
Did you mean displaying values in jiffies in /proc/mounts? Wouldn't it
be confusing for users to see such a higher numbers (usually) when they
had used a simple 2 digit number for e.g. during mount?
--
Suresh Jayaraman
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