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Subject: Re: [PATCH v27 3/4] mm/page_poison: expose page_poisoning_enabled to kernel modules
On 02/08/2018 02:34 AM, Michael S. Tsirkin wrote:
On Wed, Feb 07, 2018 at 02:54:30PM +0800, Wei Wang wrote:In some usages, e.g. virtio-balloon, a kernel module needs to know if page poisoning is in use. This patch exposes the page_poisoning_enabled function to kernel modules. Signed-off-by: Wei Wang <wei.w.wang@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michael S. Tsirkin <mst@redhat.com> --- mm/page_poison.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/page_poison.c b/mm/page_poison.c index e83fd44..c08d02a 100644 --- a/mm/page_poison.c +++ b/mm/page_poison.c @@ -30,6 +30,11 @@ bool page_poisoning_enabled(void) debug_pagealloc_enabled())); }+/**+ * page_poisoning_enabled - check if page poisoning is enabled + * + * Return true if page poisoning is enabled, or false if not. + */ static void poison_page(struct page *page) { void *addr = kmap_atomic(page); @@ -37,6 +42,7 @@ static void poison_page(struct page *page) memset(addr, PAGE_POISON, PAGE_SIZE); kunmap_atomic(addr); } +EXPORT_SYMBOL_GPL(page_poisoning_enabled);static void poison_pages(struct page *page, int n){Looks like both the comment and the export are in the wrong place.
Thanks. Will be more careful.
I'm a bit concerned that callers also in fact poke at the PAGE_POISON - exporting that seems to be more of an accident as it's only used without page_poisoning.c - it might be better to have page_poisoning_enabled get u8 * and set it.
PAGE_POISON is a macro defined in the header, why would callers using it be a concern?
Do you suggest to have: bool page_poisoning_get(u8 *val) { if (page_poisoning_enabled()) { *val = PAGE_POISON; return true; } return false; } EXPORT_SYMBOL_GPL(page_poisoning_get); Best, Wei
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