Messages in this thread | | | Date | Thu, 22 Feb 2007 12:36:24 -0500 | From | Peter Staubach <> | Subject | Re: [PATCH] update ctime and mtime for mmaped write |
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Miklos Szeredi wrote: >>>>> Inspired by Peter Staubach's patch and the resulting comments. >>>>> >>>>> >>>>> >>>>> >>>> An updated version of the original patch was submitted to LKML >>>> yesterday... :-) >>>> >>>> >>> Strange coincidence :) >>> >>> >>> >>>>> file = vma->vm_file; >>>>> start = vma->vm_end; >>>>> + mapping_update_time(file); >>>>> if ((flags & MS_SYNC) && file && >>>>> (vma->vm_flags & VM_SHARED)) { >>>>> get_file(file); >>>>> >>>>> >>>>> >>>> It seems to me that this might lead to file times being updated for >>>> non-MAP_SHARED mappings. >>>> >>>> >>> In theory no, because the COW-ed pages become anonymous and are not >>> part of the original mapping any more. >>> >>> >>> >> I must profess to having a incomplete understanding of all of this >> support, but then why would it be necessary to test VM_SHARED at >> this point in msync()? >> > > That's basically just an optimization. If it wasn't there, then data > from a another (shared) mapping could be written back, which is not > wrong, but not required either. > > >> I ran into problems early on with file times being updated incorrectly >> so I am a little sensitive this aspect. >> >> >>>>> +int set_page_dirty_mapping(struct page *page); >>>>> >>>>> >>>>> >>>> This aspect of the design seems intrusive to me. I didn't see a strong >>>> reason to introduce new versions of many of the routines just to handle >>>> these semantics. What motivated this part of your design? Why the new >>>> _mapping versions of routines? >>>> >>>> >>> Because there's no way to know inside the set_page_dirty() functions >>> if the dirtying comes from a memory mapping or from a modification >>> through a normal write(). And they have different semantics, for >>> write() the modification times are updated immediately. >>> >> Perhaps I didn't understand what page_mapped() does, but it does seem to >> have the right semantics as far as I could see. >> > > The problems will start, when you have a file that is both mapped and > modified with write(). Then the dirying from the write() will set the > flag, and that will have undesirable consequences.
I don't think that I quite follow the logic. The dirtying from write() will set the flag, but then the mtime will get updated and the flag will be cleared by the hook in file_update_time(). Right?
Thanx...
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