On Mon, Aug 31, 2009 at 12:00:06PM +0530, Aneesh Kumar K.V wrote: > Below are the possibilities i looked at > > a) mmap with no parallel write to the same offset. That would mean > we don't have attached buffer heads because nobody attach buffer > heads to the page. > > b) mmap happening to the hole. The buffer heads are not mapped. > > c) mmap with parallel write to the same offset. The parallel write > did attach mapped buffer heads to the same page. So we should find > all buffer heads mapped in the above case. > > if we will find buffer heads already be mapped in many workloads then > i guess it make sense to add page lock. It will also avoid the > journal_start that we do in write_begin. I will redo the patch The usage case I was worried about is the one where we are mmap'ing an existing file (say, like an Oracle or DB2 table space, or a berkdb database file), and we are writing into already allocated blocks. In that case (which does use these code paths, right?) the second time we write a particular page, the buffer heads will already be mapped. For database applications where we aren't loading a table, but just making changes to an already instantiated table, the buffer heads would be mapped most of the time, would they not? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
