rgw: limit rgw_gc_max_objs to RGW_SHARDS_PRIME_1

[xelexin]

Don't allow GC to process more gc ojects than RGW_SHARDS_PRIME_1

Fixes: https://tracker.ceph.com/issues/49321
Signed-off-by: Rafał Wądołowski rwadolowski@cloudferro.com

[mattbenjamin]

this slightly scrambles indentation, maybe try to align all parts of the ctor-initializer list uniformly?

[xelexin]

sure, done

[mattbenjamin]

how does this enforce limit on rgw_gc_max_objs?

[xelexin]

it will not allow to process over rgw_shards_max() value. Without this change, if we set rgw_gc_max_objs for 70000, the RGWGC::remove tries to gc_aio_operate operate on not existent objects

[mattbenjamin]

this reserves space for thus many elements, right? is that needed because we're using emplace? do we really want to reserve the max, though?

[mattbenjamin]

i.e., would it make sense to enforce a max -size-, and reject an attempt to reshard to a larger size? separately, maybe we could avoid the pre-sizing optimization, or else adjust things around it to avoid expecting the current max size?

[xelexin]

Looking at the code, we're currently allocating "unlimited" (according to configuration option) remove_tags and tag_io_size. This reserve won't allow to allocate more than RGW_SHARDS_PRIME_1. We have a lot of static references to these vectors, so yes I'm agree that RGWGCIOManager should be refactored, but this require more work. As for now I think this fix will block, deletion of objects over v RGW_SHARDS_PRIME_1.

[cbodley]

i don't understand this change to use reserve() instead of constructing the vector with a given size. this leaves the vector's size() at 0, meaning that:

• all attempts to index it will be out of bounds:

auto& rt = remove_tags[index];

• for-loops will iterate over an empty vector:

  void flush_remove_tags() {
    int index = 0;
    for (auto& rt : remove_tags) {

instead, i would just default-construct the empty vectors, and wait to resize them until initialize():

 void RGWGC::initialize(CephContext *_cct, RGWRados *_store) {
   cct = _cct;
   store = _store;
 
   max_objs = min(static_cast<int>(cct->_conf->rgw_gc_max_objs), rgw_shards_max());
+  remove_tags.resize(max_objs);
+  tag_io_size.resize(max_objs);

[mattbenjamin]

@cbodley thank you

[xelexin]

@cbodley sure, resize is better, I placed it under constructor of IOManager, because the RGWGC::initialize doesn't know about it

[mattbenjamin]

looks good

[harishmunjulur]

https://trello.com/c/DoAG4CDA

http://pulpito.ceph.com:80/hmunjulu-2021-03-03_05:40:02-rgw-wip-hmunjulu02-testing-2021-03-02-1939-distro-basic-smithi/