> -----Original Message----- > From: Waiman Long [mailto:longman@xxxxxxxxxx] > Sent: Monday, August 21, 2017 9:35 PM > To: Wangkai (Kevin,C); Alexander Viro; Jonathan Corbet > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; > linux-fsdevel@xxxxxxxxxxxxxxx; Paul E. McKenney; Andrew Morton; Ingo Molnar; > Miklos Szeredi; Matthew Wilcox; Larry Woodman; James Bottomley > Subject: Re: [PATCH v3 0/5] fs/dcache: Limit # of negative dentries > > On 08/20/2017 11:23 PM, Wangkai (Kevin,C) wrote: > > > > Yes, I have add some trace info for the dentry state changed, with dentry flag > and reference count: > > > > File create: > > [ 42.636675] dentry [xxxx_1234] 0xffff880230be8180 flag 0x0 ref 1 ev > dentry alloc > > File close: > > [ 42.637421] dentry [xxxx_1234] 0xffff880230be8180 flag 0x4800c0 ref 0 > ev dput called > > > > Unlink lookup: > > [ 244.658086] dentry [xxxx_1234] 0xffff880230be8180 flag 0x4800c0 ref > > 1 ev d_lookup Unlink d_delete: > > [ 244.658254] dentry [xxxx_1234] 0xffff880230be8180 flag 0x800c0 ref > > 1 ev d_lockref ref 1 Unlink dput: > > [ 244.658438] dentry [xxxx_1234] 0xffff880230be8180 flag 0x800c0 ref > > 0 ev dput called > > > > The end, dentry's flag stay at 0x800c0, but this dentry was not freed, > > keeped by the dcache as unused, After tens of thousands of the > > dentries slow down the dentry lookup performance, kernel memory usage > Keep high. > > > > Regards, > > Kevin > > That is expected. The kernel does not get rid of negative dentries until the > shrinker is called because of memory pressure. Negative dentries do help to > improve file lookup performance. However, too much of negative dentries > suppress the amount of free memory available for other use. > That is why I send out my patch to limit the number of negative dentries > outstanding. > I think there are two issue: 1. when a file was removed, the dentry should be deleted, this is as a bug, if the Dentry memory cannot be reclaimed, there is a memory leak. 2. limit the dentries number can improve when there were lots of files operations, And all the files were valid. Regards, Kevin
