md/r5cache: handle alloc_page failure
RMW of r5c write back cache uses an extra page to store old data for prexor. handle_stripe_dirtying() allocates this page by calling alloc_page(). However, alloc_page() may fail. To handle alloc_page() failures, this patch adds an extra page to disk_info. When alloc_page fails, handle_stripe() trys to use these pages. When these pages are used by other stripe (R5C_EXTRA_PAGE_IN_USE), the stripe is added to delayed_list. Signed-off-by: Song Liu <songliubraving@fb.com> Reviewed-by: NeilBrown <neilb@suse.com> Signed-off-by: Shaohua Li <shli@fb.com>
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