Messages in this thread | | | Date | Thu, 17 Sep 2009 21:21:37 -0700 | From | Badari Pulavarty <> | Subject | Re: Is nobh code still useful? |
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Jan Kara wrote: > Hi, > > during my page_mkwrite() work, I've looked at who uses nobh_ versions of > various functions in fs/buffer.c. It seems only ext2 and jfs use them. ext3 > uses them only from writepage() (which means we needn't attach buffers to a > page when it was written via mmap in writeback mode) and ext4 tries to use > them but in fact it's nop because it always attaches buffers to the page > earlier. So it's not really widely used, there's quite some code to support > it (including one page flag), and it also slightly complicates my > page_mkwrite() fixes. > So I wanted to ask does somebody actually remember what it is good for? > Buffer heads obviously consume some memory so was that the reason? OTOH we > have to map the page whenever we write to it or send it to disk via > writepage(). > > Originally it was supported on ext2. I added support nobh support for ext3. At that time, the main issue/complaint was that, these bufferheads consume memory from ZONE_NORMAL causing memory pressure on 32-bit (i386) configurations.
Thanks, Badari
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