Hi Andrew, Thanks for your comments. > On Thu, 20 Nov 2008 09:27:11 +0900 > Toshiyuki Okajima <toshi.okajima@xxxxxxxxxxxxxx> wrote: <SNIP> > > I'm scratching my head trying to work out why we never encountered and > fixed this before. > Is it possible that you have a very large number of filesystems > mounted, and/or that they have large journals? Yes, I think it happen more easily under those conditions. Actually, I encountered this situation if conditions were: - on the x86 architecture (The size of Normal zone is only 800MB even if the huge memory (more than 4GB) install.) - reserving the big memory (more than 100MB) for the kdump kernel. (The memory obtains from Normal Zone.) - mounting the large number of ext3 filesystems (more than 50). And the following operations were done: - many I/Os were issued to many filesystems sequentially and continuously. (They made many journal_heads (and buffer_heads). => they were metadata.) - issuing the I/Os to many filesystems were stopped. (This caused many metadata to remain.) By their operations, the number of remaining the journal_heads was more than 100000 (They occupied 400MB (The same number of buffer_heads remained and the block size was 4096B)). We cannot release those journal_heads because checkpointing the transactions are not executed till some I/Os are issued to the filesystems or the filesystems were unmounting. And many other slab caches which couldn't be released occupied about 300MB. Therefore about 800MB memory couldn't be released. As a result, there was no room in the Normal zone. I think you could not encounter it because you haven't done such the following: - You reserve the big memory for the kdump kernel. - You issue many I/Os to each ext3 filesystem sequentially and continuously, and then you never issue some I/Os to the filesystems at all afterwards. (Especially, you do the operations which causes many metadata to remain. Example: Delete many files which are huge.) > Would it not be more logical if the ->client_releasepage function > pointer were a member of the blockdev address_space_operations, rather > than some random field in the blockdev inode? That arrangement might > well be reused in the future, when some other address_space needs to > talk to a different address_space to make a page reclaimable. I think it logical to replace a default ->releasepage with a function pointer which a client (FS) passed, but I don't think it logical to add a new member function in address space in order to release a client page. Because new function is called from ->releasepage, so I think this function pointer should not be put in the same level as the releasepage of address space. Though, it is difficult to replace ->releasepage member with a client function because there is no exclusive operation while this function is calling. So, I made this patch (without replacing ->releasepage). How about my thought? Best Regards, Toshiyuki Okajima -- 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
