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    SubjectRe: [PATCH v3 2/8] mm/debug-pagealloc: prepare boottime configurable on/off
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    Joonsoo,

    On Mon, 2014-11-24 at 17:15 +0900, Joonsoo Kim wrote:
    > Until now, debug-pagealloc needs extra flags in struct page, so we need
    > to recompile whole source code when we decide to use it. This is really
    > painful, because it takes some time to recompile and sometimes rebuild is
    > not possible due to third party module depending on struct page.
    > So, we can't use this good feature in many cases.
    >
    > Now, we have the page extension feature that allows us to insert
    > extra flags to outside of struct page. This gets rid of third party module
    > issue mentioned above. And, this allows us to determine if we need extra
    > memory for this page extension in boottime. With these property, we can
    > avoid using debug-pagealloc in boottime with low computational overhead
    > in the kernel built with CONFIG_DEBUG_PAGEALLOC. This will help our
    > development process greatly.
    >
    > This patch is the preparation step to achive above goal. debug-pagealloc
    > originally uses extra field of struct page, but, after this patch, it
    > will use field of struct page_ext. Because memory for page_ext is
    > allocated later than initialization of page allocator in CONFIG_SPARSEMEM,
    > we should disable debug-pagealloc feature temporarily until initialization
    > of page_ext. This patch implements this.
    >
    > v2: fix compile error on CONFIG_PAGE_POISONING
    >
    > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

    This patch is included in today's linux-next (ie, next-2o0141127) as
    commit 1e491e9be4c9 ("mm/debug-pagealloc: prepare boottime configurable
    on/off").

    > [...]
    >
    > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
    > index 33a8acf..c7b22e7 100644
    > --- a/include/linux/mm_types.h
    > +++ b/include/linux/mm_types.h
    > @@ -10,7 +10,6 @@
    > #include <linux/rwsem.h>
    > #include <linux/completion.h>
    > #include <linux/cpumask.h>
    > -#include <linux/page-debug-flags.h>
    > #include <linux/uprobes.h>
    > #include <linux/page-flags-layout.h>
    > #include <asm/page.h>
    > @@ -186,9 +185,6 @@ struct page {
    > void *virtual; /* Kernel virtual address (NULL if
    > not kmapped, ie. highmem) */
    > #endif /* WANT_PAGE_VIRTUAL */
    > -#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
    > - unsigned long debug_flags; /* Use atomic bitops on this */
    > -#endif
    >
    > #ifdef CONFIG_KMEMCHECK
    > /*
    > diff --git a/include/linux/page-debug-flags.h b/include/linux/page-debug-flags.h
    > deleted file mode 100644
    > index 22691f61..0000000
    > --- a/include/linux/page-debug-flags.h
    > +++ /dev/null
    > @@ -1,32 +0,0 @@
    > -#ifndef LINUX_PAGE_DEBUG_FLAGS_H
    > -#define LINUX_PAGE_DEBUG_FLAGS_H
    > -
    > -/*
    > - * page->debug_flags bits:
    > - *
    > - * PAGE_DEBUG_FLAG_POISON is set for poisoned pages. This is used to
    > - * implement generic debug pagealloc feature. The pages are filled with
    > - * poison patterns and set this flag after free_pages(). The poisoned
    > - * pages are verified whether the patterns are not corrupted and clear
    > - * the flag before alloc_pages().
    > - */
    > -
    > -enum page_debug_flags {
    > - PAGE_DEBUG_FLAG_POISON, /* Page is poisoned */
    > - PAGE_DEBUG_FLAG_GUARD,
    > -};
    > -
    > -/*
    > - * Ensure that CONFIG_WANT_PAGE_DEBUG_FLAGS reliably
    > - * gets turned off when no debug features are enabling it!
    > - */
    > -
    > -#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
    > -#if !defined(CONFIG_PAGE_POISONING) && \
    > - !defined(CONFIG_PAGE_GUARD) \
    > -/* && !defined(CONFIG_PAGE_DEBUG_SOMETHING_ELSE) && ... */
    > -#error WANT_PAGE_DEBUG_FLAGS is turned on with no debug features!
    > -#endif
    > -#endif /* CONFIG_WANT_PAGE_DEBUG_FLAGS */
    > -
    > -#endif /* LINUX_PAGE_DEBUG_FLAGS_H */

    This remove all uses of CONFIG_WANT_PAGE_DEBUG_FLAGS and
    CONFIG_PAGE_GUARD. So the Kconfig symbols WANT_PAGE_DEBUG_FLAGS and
    PAGE_GUARD are now unused.

    Should I submit the trivial patch to remove these symbols or is a patch
    that does that queued already?


    Paul Bolle



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