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    SubjectRe: [PATCH 12/30] mm: memory reserve management
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    On Tue, 2008-08-12 at 17:46 +1000, Neil Brown wrote:
    > On Thursday July 24, a.p.zijlstra@chello.nl wrote:
    > > Generic reserve management code.
    > >
    > > It provides methods to reserve and charge. Upon this, generic alloc/free style
    > > reserve pools could be build, which could fully replace mempool_t
    > > functionality.
    >
    > More comments on this patch .....
    >
    > > +void *___kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip,
    > > + struct mem_reserve *res, int *emerg);
    > > +
    > > +static inline
    > > +void *__kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip,
    > > + struct mem_reserve *res, int *emerg)
    > > +{
    > > + void *obj;
    > > +
    > > + obj = __kmalloc_node_track_caller(size,
    > > + flags | __GFP_NOMEMALLOC | __GFP_NOWARN, node, ip);
    > > + if (!obj)
    > > + obj = ___kmalloc_reserve(size, flags, node, ip, res, emerg);
    > > +
    > > + return obj;
    > > +}
    > > +
    > > +#define kmalloc_reserve(size, gfp, node, res, emerg) \
    > > + __kmalloc_reserve(size, gfp, node, \
    > > + __builtin_return_address(0), res, emerg)
    > > +
    > ......
    > > +/*
    > > + * alloc wrappers
    > > + */
    > > +
    > > +void *___kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip,
    > > + struct mem_reserve *res, int *emerg)
    > > +{
    > > + void *obj;
    > > + gfp_t gfp;
    > > +
    > > + gfp = flags | __GFP_NOMEMALLOC | __GFP_NOWARN;
    > > + obj = __kmalloc_node_track_caller(size, gfp, node, ip);
    > > +
    > > + if (obj || !(gfp_to_alloc_flags(flags) & ALLOC_NO_WATERMARKS))
    > > + goto out;
    > > +
    > > + if (res && !mem_reserve_kmalloc_charge(res, size)) {
    > > + if (!(flags & __GFP_WAIT))
    > > + goto out;
    > > +
    > > + wait_event(res->waitqueue,
    > > + mem_reserve_kmalloc_charge(res, size));
    > > +
    > > + obj = __kmalloc_node_track_caller(size, gfp, node, ip);
    > > + if (obj) {
    > > + mem_reserve_kmalloc_charge(res, -size);
    > > + goto out;
    > > + }
    > > + }
    > > +
    > > + obj = __kmalloc_node_track_caller(size, flags, node, ip);
    > > + WARN_ON(!obj);
    > > + if (emerg)
    > > + *emerg |= 1;
    > > +
    > > +out:
    > > + return obj;
    > > +}
    >
    > Two comments to be precise.
    >
    > 1/ __kmalloc_reserve attempts a __GFP_NOMEMALLOC allocation, and then
    > if that fails, ___kmalloc_reserve immediately tries again.
    > Is that pointless? Should the second one be removed?

    Pretty pointless yes, except that it made ___kmalloc_reserve a nicer
    function to read, and as its an utter slow path I couldn't be arsed to
    optimize :-)

    > 2/ mem_reserve_kmalloc_charge appears to assume that the 'mem_reserve'
    > has been 'connected' and so is active.

    Hmm, that would be __mem_reserve_charge() then, because the callers
    don't do much.

    > While callers probably only set GFP_MEMALLOC in cases where the
    > mem_reserve is connected, ALLOC_NO_WATERMARKS could get via
    > PF_MEMALLOC so we could end up calling mem_reserve_kmalloc_charge
    > when the mem_reserve is not connected.

    Right..

    > That seems to be 'odd' at least.
    > It might even be 'wrong' as mem_reserve_connect doesn't add the
    > usage of the child to the parent - only the ->pages and ->limit.
    >
    > What is your position on this? Mine is "still slightly confused".

    Uhmm,. good point. Let me ponder this while I go for breakfast ;-)





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