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Date: Tue, 7 Apr 2009 19:10:29 -0500 From: Russ Anderson <rja@....com> To: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org Cc: Russ Anderson <rja@....com> Subject: [PATCH 0/2] Migrate data off physical pages with corrected memory errors Purpose: Physical memory with corrected errors may decay over time into uncorrectable errors. The purpose of this patch is to move the data off pages with correctable memory errors before the memory goes bad. This patch set applies on top of Andi Kleen's POISON patch set. The patches: [1/2] Avoid putting a bad page back on the LRU. Avoid putting a bad page back on the LRU after migrating the data to a new page. The reference count on the bad page is not decremented to zero to avoid it being reallocated. [2/3] Call migration code on correctable errors This patch has ia64 specific changes. It connects the CPE handler to the page migration code. It is implemented as a kernel loadable module, similar to the mca recovery code (mca_recovery.ko), so that it can be removed to turn off the feature. Create /sys/kernel/badram to print page discard information and to free bad pages. Comments: There is always an issue of how agressive the code should be on migrating pages. This patch uses /sys/firmware/badram/migrate_threshold to adjust the number of correctable errors before migrating a page. Only pages that can be isolated on the LRU are migrated. Other pages, such as compound pages, are not migrated. That functionality could be a future enhancement. /sys/kernel/badram/bad_pages is used to display information about the bad memory. The interface can be used to free pages marked bad. Sample output: This is sample output from a system with a DIMM that has correctable errors at many addresses. linux> ls /sys/firmware/badram/ bad_pages cmc_polling_threshold cpe_polling_threshold migrate_threshold linux> cat /sys/firmware/badram/bad_pages Memory marked bad: 704 kB Pages marked bad: 11 Unable to isolate on LRU: 1 Unable to migrate: 0 Already marked bad: 2 Already on list: 0 List of bad physical pages 0x06871110000 0x06014820000 0x26003b20000 0x26005380000 0x26005390000 0x260053a0000 0x260053b0000 0x260052f0000 0x26004bf0000 0x26004af0000 0x26005330000 // Free one of the pages linux> echo 0x06014820000 > /sys/firmware/badram/bad_pages // 10 pages remain on the list linux> cat /sys/firmware/badram/bad_pages Memory marked bad: 640 kB Pages marked bad: 10 Unable to isolate on LRU: 1 Unable to migrate: 0 Already marked bad: 2 Already on list: 0 List of bad physical pages 0x06871110000 0x26003b20000 0x26005380000 0x26005390000 0x260053a0000 0x260053b0000 0x260052f0000 0x26004bf0000 0x26004af0000 0x26005330000 // Free all the bad pages linux> echo 0 > /sys/firmware/badram/bad_pages // All the pages are freed linux> cat /sys/firmware/badram/bad_pages Memory marked bad: 0 kB Pages marked bad: 0 Unable to isolate on LRU: 1 Unable to migrate: 0 Already marked bad: 2 Already on list: 0 List of bad physical pages Flow of the code description (while testing on IA64): 1) A user level application test program allocates memory and passes the virtual address of the memory to the error injection driver. 2) The error injection driver converts the virtual address to physical, functions the Altix hardware to modify the ECC for the physical page, creating a correctable error, and returns to the user application. 3) The user application reads the memory. 4) The Altix hardware detects the correctable error and interrupts prom. SAL builds a CPU error record, then sends a CPE interrupt to linux. 5) The linux CPE handler calls the cpe_migrate module (if installed). 6) cpe_setup_migrate parses the physical address from the CPE record and adds the address to the migrate list (if not already on the list) and wakes up a kernel thread (cpe_process_queue). 7) cpe_process_queue checks if the threshold has been exceeded and calls ia64_mca_cpe_move_page. 8) ia64_mca_cpe_move_page validates the physical address, converts to page, sets PG_memerror flag and calls the migration code (migrate_prep(), isolate_lru_page(), and migrate_pages(). If the page migrates successfully, the bad page is added to badpagelist. 9) Because PG_Poison is set, the bad page is not added back on the LRU by avoiding calls to move_to_lru(). Avoiding move_to_lru() prevents the page count from being decremented to zero. 10) If the page fails to migrate, PG_Poison is cleared and the page returned to the LRU. If another correctable error occurs on the page another attempt will be made to migrate it. -- Russ Anderson, OS RAS/Partitioning Project Lead SGI - Silicon Graphics Inc rja@....com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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