什么可能是nfs_lookup请求数量很高的原因?

由于在我的NFS客户端和NFS服务器上最近进行的Linux内核升级(在Debian Wheezy上是3.2.78),我看到从客户端到服务器的nfs_lookup请求的数量增加很多(10到20倍)。 这对运行在我的NFS客户端上的应用程序(apache + php-fpm)造成巨大的性能下降。

什么可能导致nfs_lookup这么高的增长?

正常运行1小时后,在其中一个客户mountstats --nfs上输出mountstats --nfs如下:

 Stats for ruchbah.nfs://membres mounted on /srv/membres: NFS mount options: rw,vers=4,rsize=1048576,wsize=1048576,namlen=255,acregmin=3,acregmax=60,acdirmin=30,acdirmax=60,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.74.13,minorversion=0,local_lock=none NFS server capabilities: caps=0x7fff,wtmult=512,dtsize=32768,bsize=0,namlen=255 NFSv4 capability flags: bm0=0xfdffbfff,bm1=0xf9be3e,acl=0x3 NFS security flavor: 1 pseudoflavor: 0 Cache events: data cache invalidated 1231 times attribute cache invalidated 23693734 times inodes synced 1790 times VFS calls: VFS requested 46296214 inode revalidations VFS requested 35900771 dentry revalidations VFS called nfs_readdir() 3678 times VFS called nfs_lookup() 35200320 times VFS called nfs_permission() 11201 times VFS called nfs_file_open() 22547 times VFS called nfs_file_flush() 1400 times VFS called nfs_lock() 7611 times VFS called nfs_fsync() 65321 times VFS called nfs_file_release() 3731 times VM calls: VFS called nfs_readpage() 856 times VFS called nfs_readpages() 6945 times VFS called nfs_writepage() 10789 times VFS called nfs_writepages() 945872 times Generic NFS counters: File size changing operations: truncating SETATTRs: 65272 extending WRITEs: 0 291 silly renames short reads: 11201 short writes: 17 NFSERR_DELAYs from server: 0 NFS byte counts: applications read 162084951 bytes via read(2) applications wrote 19636930 bytes via write(2) applications read 0 bytes via O_DIRECT read(2) applications wrote 0 bytes via O_DIRECT write(2) client read 152501261 bytes via NFS READ client wrote 20783074 bytes via NFS WRITE 

VFS调用的数量(尤其是nfs_lookup)非常高。 caching属性失效也exception高。 客户端主要使用NFS挂载来读取数据。