Messages in this thread | | | Date | Tue, 16 Jan 2001 21:17:37 +0100 (CET) | From | Urban Widmark <> | Subject | Re: Oops with 4GB memory setting in 2.4.0 stable |
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On Tue, 16 Jan 2001, Petr Vandrovec wrote:
> smb_get_dircache looks suspicious to me, as it can try to map unlimited > number of pages with kmap. And kmaps are not unlimited resource... > You have 512 kmaps, but one SMBFS cache page can contain about 504 > pages... So two smbfs cached directories can consume all your kmaps, > dying then in endless loop in mm/highmem.c:map_new_virtual().
The smbfs dircache needs to find/kmap all of its cache pages since the entries in it are variable length and the way it is called. It would be nice to change that.
I haven't looked at all your detailed comments yet. They may not matter if the many kmaps are a problem.
The ncpfs code puts 'struct dentry *' in it's cache pages. Fixed size entries makes it easy to know which page you need to start reading from, so only one kmap is needed. That looks simpler so I want to steal it, except ...
ncpfs ends up calling d_validate to verify that the dentry is sane. But how can it know that the dentry is the right one? I thought that dentries could be removed/reused by someone at will (d_count will be 0 because of the dput in ncp_fill_cache, no?). Why isn't it possible for someone to write a new dentry where the old one was.
fs/ncpfs/dir.c:ncp_d_validate() calls valid = d_validate(dentry, dentry->d_parent, dentry->d_name.hash, len);
all values are taken from the dentry pointer on the cache page (including len). d_validate verifies that d_hash() points to a list and it searches the list for dentry. How do you know that it is the same dentry that was put in the cache and not someone elses dentry?
> But I personally do not use neither smbfs nor PAE, so what I can say...
A whole lot, thanks. Especially for the kmap info.
Now if someone could explain the dentry pointers ... what am I missing?
/Urban
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