> 2022年9月19日 19:42，Andrea Tomassetti <andrea.tomassetti-opensource@xxxxxxxx> 写道：
>
> Hi Coly,
> have you had any time to take a look at this? Do you prefer if I send the patch as a separate thread?
>
> Thank you very much,
> Andrea
Yes, it is on my queue, just after I finish my tasks on hand, I will take a look on it.
Thanks.
Coly Li
>
> On 8/9/22 10:32, Andrea Tomassetti wrote:
>> From 59787372cf21af0b79e895578ae05b6586dfeb09 Mon Sep 17 00:00:00 2001
>> From: Andrea Tomassetti <andrea.tomassetti-opensource@xxxxxxxx>
>> Date: Thu, 8 Sep 2022 09:47:55 +0200
>> Subject: [PATCH] bcache: Add support for live resize of backing devices
>> Signed-off-by: Andrea Tomassetti <andrea.tomassetti-opensource@xxxxxxxx>
>> ---
>> Hi Coly,
>> Here is the first version of the patch. There are some points I noted down
>> that I would like to discuss with you:
>> - I found it pretty convenient to hook the call of the new added function
>> inside the `register_bcache`. In fact, every time (at least from my
>> understandings) a disk changes size, it will trigger a new probe and,
>> thus, `register_bcache` will be triggered. The only inconvenient
>> is that, in case of success, the function will output
>> `error: capacity changed` even if it's not really an error.
>> - I'm using `kvrealloc`, introduced in kernel version 5.15, to resize
>> `stripe_sectors_dirty` and `full_dirty_stripes`. It shouldn't be a
>> problem, right?
>> - There is some reused code between this new function and
>> `bcache_device_init`. Maybe I can move `const size_t max_stripes` to
>> a broader scope or make it a macro, what do you think?
>> Thank you very much,
>> Andrea
>> drivers/md/bcache/super.c | 75 ++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 74 insertions(+), 1 deletion(-)
>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> index ba3909bb6bea..9a77caf2a18f 100644
>> --- a/drivers/md/bcache/super.c
>> +++ b/drivers/md/bcache/super.c
>> @@ -2443,6 +2443,76 @@ static bool bch_is_open(dev_t dev)
>> return bch_is_open_cache(dev) || bch_is_open_backing(dev);
>> }
>> +static bool bch_update_capacity(dev_t dev)
>> +{
>> + const size_t max_stripes = min_t(size_t, INT_MAX,
>> + SIZE_MAX / sizeof(atomic_t));
>> +
>> + uint64_t n, n_old;
>> + int nr_stripes_old;
>> + bool res = false;
>> +
>> + struct bcache_device *d;
>> + struct cache_set *c, *tc;
>> + struct cached_dev *dcp, *t, *dc = NULL;
>> +
>> + uint64_t parent_nr_sectors;
>> +
>> + list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
>> + list_for_each_entry_safe(dcp, t, &c->cached_devs, list)
>> + if (dcp->bdev->bd_dev == dev) {
>> + dc = dcp;
>> + goto dc_found;
>> + }
>> +
>> +dc_found:
>> + if (!dc)
>> + return false;
>> +
>> + parent_nr_sectors = bdev_nr_sectors(dc->bdev) - dc->sb.data_offset;
>> +
>> + if (parent_nr_sectors == bdev_nr_sectors(dc->disk.disk->part0))
>> + return false;
>> +
>> + if (!set_capacity_and_notify(dc->disk.disk, parent_nr_sectors))
>> + return false;
>> +
>> + d = &dc->disk;
>> +
>> + /* Force cached device sectors re-calc */
>> + calc_cached_dev_sectors(d->c);
>> +
>> + /* Block writeback thread */
>> + down_write(&dc->writeback_lock);
>> + nr_stripes_old = d->nr_stripes;
>> + n = DIV_ROUND_UP_ULL(parent_nr_sectors, d->stripe_size);
>> + if (!n || n > max_stripes) {
>> + pr_err("nr_stripes too large or invalid: %llu (start sector beyond end of disk?)\n",
>> + n);
>> + goto unblock_and_exit;
>> + }
>> + d->nr_stripes = n;
>> +
>> + n = d->nr_stripes * sizeof(atomic_t);
>> + n_old = nr_stripes_old * sizeof(atomic_t);
>> + d->stripe_sectors_dirty = kvrealloc(d->stripe_sectors_dirty, n_old,
>> + n, GFP_KERNEL);
>> + if (!d->stripe_sectors_dirty)
>> + goto unblock_and_exit;
>> +
>> + n = BITS_TO_LONGS(d->nr_stripes) * sizeof(unsigned long);
>> + n_old = BITS_TO_LONGS(nr_stripes_old) * sizeof(unsigned long);
>> + d->full_dirty_stripes = kvrealloc(d->full_dirty_stripes, n_old, n, GFP_KERNEL);
>> + if (!d->full_dirty_stripes)
>> + goto unblock_and_exit;
>> +
>> + res = true;
>> +
>> +unblock_and_exit:
>> + up_write(&dc->writeback_lock);
>> + return res;
>> +}
>> +
>> struct async_reg_args {
>> struct delayed_work reg_work;
>> char *path;
>> @@ -2569,7 +2639,10 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>> mutex_lock(&bch_register_lock);
>> if (lookup_bdev(strim(path), &dev) == 0 &&
>> bch_is_open(dev))
>> - err = "device already registered";
>> + if (bch_update_capacity(dev))
>> + err = "capacity changed";
>> + else
>> + err = "device already registered";
>> else
>> err = "device busy";
>> mutex_unlock(&bch_register_lock);
>> --
>> 2.37.3
>> On 6/9/22 15:22, Andrea Tomassetti wrote:
>>> Hi Coly,
>>> I have finally some time to work on the patch. I already have a first
>>> prototype that seems to work but, before sending it, I would like to
>>> ask you two questions:
>>> 1. Inspecting the code, I found that the only lock mechanism is the
>>> writeback_lock semaphore. Am I correct?
>>> 2. How can I effectively test my patch? So far I'm doing something like this:
>>> a. make-bcache --writeback -B /dev/vdb -C /dev/vdc
>>> b. mkfs.xfs /dev/bcache0
>>> c. dd if=/dev/random of=/mnt/random bs=1M count=1000
>>> d. md5sum /mnt/random | tee /mnt/random.md5
>>> e. live resize the disk and repeat c. and d.
>>> f. umount/reboot/remount and check that the md5 hashes are correct
>>>
>>> Any suggestions?
>>>
>>> Thank you very much,
>>> Andrea
>>>
>>> On Fri, Aug 5, 2022 at 9:38 PM Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> wrote:
>>>>
>>>> On Wed, 3 Aug 2022, Andrea Tomassetti wrote:
>>>>> Hi Coly,
>>>>> In one of our previous emails you said that
>>>>>> Currently bcache doesn’t support cache or backing device resize
>>>>>
>>>>> I was investigating this point and I actually found a solution. I
>>>>> briefly tested it and it seems to work fine.
>>>>> Basically what I'm doing is:
>>>>> 1. Check if there's any discrepancy between the nr of sectors
>>>>> reported by the bcache backing device (holder) and the nr of sectors
>>>>> reported by its parent (slave).
>>>>> 2. If the number of sectors of the two devices are not the same,
>>>>> then call set_capacity_and_notify on the bcache device.
>>>>> 3. From user space, depending on the fs used, grow the fs with some
>>>>> utility (e.g. xfs_growfs)
>>>>>
>>>>> This works without any need of unmounting the mounted fs nor stopping
>>>>> the bcache backing device.
>>>>
>>>> Well done! +1, would love to see a patch for this!
>>>>
>>>>
>>>>> So my question is: am I missing something? Can this live resize cause
>>>>> some problems (e.g. data loss)? Would it be useful if I send a patch on
>>>>> this?
>>>>
>>>> A while a go we looked into doing this. Here is the summary of our
>>>> findings, not sure if there are any other considerations:
>>>>
>>>> 1. Create a sysfs file like /sys/block/bcache0/bcache/resize to trigger
>>>> resize on echo 1 >.
>>>> 2. Refactor the set_capacity() bits from bcache_device_init() into its
>>>> own function.
>>>> 3. Put locks around bcache_device.full_dirty_stripes and
>>>> bcache_device.stripe_sectors_dirty. Re-alloc+copy+free and zero the
>>>> new bytes at the end. Grep where bcache_device.full_dirty_stripes is
>>>> used and make sure it is locked appropriately, probably in the
>>>> writeback thread, maybe other places too.
>>>>
>>>> The cachedev's don't know anything about the bdev size, so (according to
>>>> Kent) they will "just work" by referencing new offsets that were
>>>> previously beyond the disk. (This is basically the same as resizing the
>>>> bdev and then unregister/re-register which is how we resize bdevs now.)
>>>>
>>>> As for resizing a cachedev, I've not looked at all---not sure about that
>>>> one. We always detach, resize, make-bcache and re-attach the new cache.
>>>> Maybe it is similarly simple, but haven't looked.
>>>>
>>>>
>>>> --
>>>> Eric Wheeler
>>>>
>>>>
>>>>
>>>>>
>>>>> Kind regards,
>>>>> Andrea
>>>>>
