Messages in this thread | | | Subject | Re: [patch 2/4 -mm] flex_array: add flex_array_clear function | From | Dave Hansen <> | Date | Mon, 24 Aug 2009 13:38:40 -0700 |
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On Mon, 2009-08-24 at 13:29 -0700, David Rientjes wrote: > On Mon, 24 Aug 2009, Dave Hansen wrote: > > > My only worry about this is that it's largely a copy-and-paste of > > flex_array_put(). If we had a function that just returned a pointer to > > 'dst', we could use that in both cases. > > > > Couldn't we implement the above with just: > > > > int flex_array_clear(struct flex_array *fa, unsigned int element_nr) > > { > > return flex_array_put(fa, element_nr, &empty_zero_page); > > } > > > > Sure, if you never increase FLEX_ARRAY_PART_SIZE. Otherwise, doing > > static char zero_part[FLEX_ARRAY_PART_SIZE] = { > [0 ... FLEX_ARRAY_PART_SIZE - 1] = 0 > }; > > and using flex_array_put(fa, element_nr, &zero_part) would work although > you're trading off cleaner, yet not more efficient, code at the cost of > FLEX_ARRAY_PART_SIZE wasted memory and memcpy() being slower than > memset().
Yeah, that's true. How about using the get() function?
int flex_array_clear(struct flex_array *fa, unsigned int element_nr) { void *element = flex_array_get(fa, element_nr); memset(element, FLEX_ARRAY_FREE, fa->element_size); }
It'll keep us from having to keep around a zero'd element.
But, I guess we could also do:
struct flex_array_part *zero_part = empty_zero_page;
And use a BUILD_BUG_ON(FLEX_ARRAY_PART_SIZE > PAGE_SIZE). But the whole point of this was to have elements that are smaller than PAGE_SIZE. Having that as a constraint doesn't seem too bad. :)
-- Dave
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