Hello, On Thu 18-12-08 14:15:25, Toshiyuki Okajima wrote: > > > > From: Toshiyuki Okajima <toshi.okajima@xxxxxxxxxxxxxx> > > > > > > > > Implement blkdev_releasepage() to release the buffer_heads and page > > > > after we release private data which belongs to a client of the block > > > > device, such as a filesystem. > > > > > > > > blkdev_releasepage() call the client's releasepage() which is > > > > registered by blkdev_register_client_releasepage() to release its > > > > private data. > > Yes, this is IMO the right fix. I'm just wondering about the fact that we > > can't block in the client_releasepage(). That seems to be caused by the fact > > that we need to be protected against client_releasepage() callback changes > > which essentially means umount, right? I'm not saying I have a better solution > > but introducing such limitation seems stupid just because of umount... > > > Difference between v2 and v3 in blkdev_releasepage: > < ret = (*ei->client_releasepage)(ei->client, page, wait); > < else > -- > > /* > > * Since we are holding a spinlock (ei->client_lock), > > * make sure the client_releasepage function > > * understands that it must not block. > > */ > > ret = (*ei->client_releasepage)(ei->client, page, > > wait & ~__GFP_WAIT); > > else > > Ask for clarification. Yes, my question was more about the original design of the patch than about the particular fix. Sorry for the confusion. > Which of the following do you mean: > 1) If using a spinlock in client_releasepage() is only for mount/umount, > this implementation is not wise. > 2) There is the fact that a spinlock is necessary for blkdev_releasepage(). > This fact prevents us from making various implementations of > client_releasepage(). > (Without a spinlock, we can implement a client_releasepage() which can release > the buffers with a sleep. As a result, it may enable more buffers release than > before.) > > There is the fact that a filesystem can be mounted on several places, > and the lock mechanism is absolutely necessary for this fact. This is the thing I was wondering about. Why exactly is the spinlock necessary for blkdev_releasepage()? I understand we have to protect reading client_releasepage() pointer because it could change but my point was that it changes only during mount / umount. > I also think we are sad that we cannot implement various implementations for > client_releasepage(). But now I cannot imagine what to do for > a client_releasepage() which can sleep, too... Regards Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
