On Tue, Apr 10, 2018 at 09:21:20AM -0500, Christopher Lameter wrote:
On Tue, 10 Apr 2018, Matthew Wilcox wrote:
__GFP_ZERO requests that the object be initialised to all-zeroes, while the purpose of a constructor is to initialise an object to a particular pattern. We cannot do both. Add a warning to catch any users who mistakenly pass a __GFP_ZERO flag when allocating a slab with a constructor.
Can we move this check out of the critical paths and check for a ctor and GFP_ZERO when calling the page allocator? F.e. in allocate_slab()?
Are you willing to have this kind of bug go uncaught for a while? In this specific case, __GFP_ZERO was only being passed on a few of the calls to kmem_cache_alloc. So we'd happily trash the constructed object any time we didn't allocate a page.
I appreciate it's a tradeoff, and we don't want to clutter the critical path unnecessarily.