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    SubjectRe: Has slab ctor operation changed? -- was [PATCH 1/1] afs: afs_alloc_inode: use kmem_cache_zalloc
    On Thu, 20 Feb 2014 22:23:15 +0000
    David Howells <dhowells@redhat.com> wrote:

    > Fabian Frederick <fabf@skynet.be> wrote:
    >
    > > afs_vnode is currently cleared with 2 memsets after allocation and
    > > 1 in constructor (afs_i_init_once).
    > > -This patch calls zalloc for explicit zero fill.
    >
    > Ummm... This patch isn't necessarily correct in the substantiative portions.
    >
    > Since afs_i_init_once() is called by the slab allocator during the course of
    > kmem_cache_alloc(), how does kmem_cache_zalloc() interact with that?

    Object of this patch was to replace any kmem_cache_alloc by kmem_cache_zalloc
    so I guess what is done in the patch v2 in afs_alloc_inode below zalloc
    would be ok (leaving ctor how it is) ?

    >
    > IIRC, it used to be that the ctor() function was called when the pages were
    > allocated to the slab - and it wasn't called again, even if the object was
    > allocated, deallocated and reallocated. This means that things like locks and
    > lists don't need reinitialising after allocation.
    >
    > So afs_i_init_once() theoretically constructs the stuff that can be reused,
    > and afs_alloc_inode() therefore has to clear the non-reusable state.
    >
    > Of course, it's possible that the slab allocator no longer works like this...
    >
    > David


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