Re: [PATCH 04/10] mm, fsdax: Refactor memory-failure handler for dax mapping

Jan Kara
2021-01-06T15:42:30Z

On Thu 31-12-20 00:55:55, Shiyang Ruan wrote:
> The current memory_failure_dev_pagemap() can only handle single-mapped
> dax page for fsdax mode. The dax page could be mapped by multiple files
> and offsets if we let reflink feature & fsdax mode work together. So,
> we refactor current implementation to support handle memory failure on
> each file and offset.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>

Overall this looks OK to me, a few comments below.

> ---
> fs/dax.c | 21 +++++++++++
> include/linux/dax.h | 1 +
> include/linux/mm.h | 9 +++++
> mm/memory-failure.c | 91 ++++++++++++++++++++++++++++++++++-----------
> 4 files changed, 100 insertions(+), 22 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 5b47834f2e1b..799210cfa687 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -378,6 +378,27 @@ static struct page *dax_busy_page(void *entry)
> return NULL;
> }
>
> +/*
> + * dax_load_pfn - Load pfn of the DAX entry corresponding to a page
> + * @mapping: The file whose entry we want to load
> + * @index: The offset where the DAX entry located in
> + *
> + * Return: pfn of the DAX entry
> + */
> +unsigned long dax_load_pfn(struct address_space *mapping, unsigned long index)
> +{
> + XA_STATE(xas, &mapping->i_pages, index);
> + void *entry;
> + unsigned long pfn;
> +
> + xas_lock_irq(&xas);
> + entry = xas_load(&xas);
> + pfn = dax_to_pfn(entry);
> + xas_unlock_irq(&xas);
> +
> + return pfn;
> +}
> +
> /*
> * dax_lock_mapping_entry - Lock the DAX entry corresponding to a page
> * @page: The page whose entry we want to lock
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b52f084aa643..89e56ceeffc7 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -150,6 +150,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
>
> struct page *dax_layout_busy_page(struct address_space *mapping);
> struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
> +unsigned long dax_load_pfn(struct address_space *mapping, unsigned long index);
> dax_entry_t dax_lock_page(struct page *page);
> void dax_unlock_page(struct page *page, dax_entry_t cookie);
> #else
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index db6ae4d3fb4e..db3059a1853e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1141,6 +1141,14 @@ static inline bool is_device_private_page(const struct page *page)
> page->pgmap->type == MEMORY_DEVICE_PRIVATE;
> }
>
> +static inline bool is_device_fsdax_page(const struct page *page)
> +{
> + return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
> + IS_ENABLED(CONFIG_DEVICE_PRIVATE) &&
> + is_zone_device_page(page) &&
> + page->pgmap->type == MEMORY_DEVICE_FS_DAX;
> +}
> +
> static inline bool is_pci_p2pdma_page(const struct page *page)
> {
> return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
> @@ -3030,6 +3038,7 @@ enum mf_flags {
> MF_MUST_KILL = 1 << 2,
> MF_SOFT_OFFLINE = 1 << 3,
> };
> +extern int mf_dax_mapping_kill_procs(struct address_space *mapping, pgoff_t index, int flags);
> extern int memory_failure(unsigned long pfn, int flags);
> extern void memory_failure_queue(unsigned long pfn, int flags);
> extern void memory_failure_queue_kick(int cpu);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 5d880d4eb9a2..37bc6e2a9564 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -56,6 +56,7 @@
> #include <linux/kfifo.h>
> #include <linux/ratelimit.h>
> #include <linux/page-isolation.h>
> +#include <linux/dax.h>
> #include "internal.h"
> #include "ras/ras_event.h"
>
> @@ -120,6 +121,9 @@ static int hwpoison_filter_dev(struct page *p)
> if (PageSlab(p))
> return -EINVAL;
>
> + if (is_device_fsdax_page(p))
> + return 0;
> +
> mapping = page_mapping(p);
> if (mapping == NULL || mapping->host == NULL)
> return -EINVAL;
> @@ -290,9 +294,8 @@ void shake_page(struct page *p, int access)
> EXPORT_SYMBOL_GPL(shake_page);
>
> static unsigned long dev_pagemap_mapping_shift(struct page *page,
> - struct vm_area_struct *vma)
> + struct vm_area_struct *vma, unsigned long address)

The 'page' argument is now unused. Drop it?

> {
> - unsigned long address = vma_address(page, vma);
> pgd_t *pgd;
> p4d_t *p4d;
> pud_t *pud;
> @@ -333,8 +336,8 @@ static unsigned long dev_pagemap_mapping_shift(struct page *page,
> * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
> */
> static void add_to_kill(struct task_struct *tsk, struct page *p,
> - struct vm_area_struct *vma,
> - struct list_head *to_kill)
> + struct address_space *mapping, pgoff_t pgoff,
> + struct vm_area_struct *vma, struct list_head *to_kill)
> {
> struct to_kill *tk;
>
> @@ -345,9 +348,12 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
> }
>
> tk->addr = page_address_in_vma(p, vma);
> - if (is_zone_device_page(p))
> - tk->size_shift = dev_pagemap_mapping_shift(p, vma);
> - else
> + if (is_zone_device_page(p)) {
> + if (is_device_fsdax_page(p))
> + tk->addr = vma->vm_start +
> + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);

It seems strange to use 'pgoff' for dax pages and not for any other page.
Why? I'd rather pass correct pgoff from all callers of add_to_kill() and
avoid this special casing...

> + tk->size_shift = dev_pagemap_mapping_shift(p, vma, tk->addr);
> + } else
> tk->size_shift = page_shift(compound_head(p));
>
> /*
> @@ -495,7 +501,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
> if (!page_mapped_in_vma(page, vma))
> continue;
> if (vma->vm_mm == t->mm)
> - add_to_kill(t, page, vma, to_kill);
> + add_to_kill(t, page, NULL, 0, vma, to_kill);
> }
> }
> read_unlock(&tasklist_lock);
> @@ -505,24 +511,19 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
> /*
> * Collect processes when the error hit a file mapped page.
> */
> -static void collect_procs_file(struct page *page, struct list_head *to_kill,
> - int force_early)
> +static void collect_procs_file(struct page *page, struct address_space *mapping,
> + pgoff_t pgoff, struct list_head *to_kill, int force_early)
> {
> struct vm_area_struct *vma;
> struct task_struct *tsk;
> - struct address_space *mapping = page->mapping;
> - pgoff_t pgoff;
>
> i_mmap_lock_read(mapping);
> read_lock(&tasklist_lock);
> - pgoff = page_to_pgoff(page);
> for_each_process(tsk) {
> struct task_struct *t = task_early_kill(tsk, force_early);
> -
> if (!t)
> continue;
> - vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
> - pgoff) {
> + vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> /*
> * Send early kill signal to tasks where a vma covers
> * the page but the corrupted page is not necessarily
> @@ -531,7 +532,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
> * to be informed of all such data corruptions.
> */
> if (vma->vm_mm == t->mm)
> - add_to_kill(t, page, vma, to_kill);
> + add_to_kill(t, page, mapping, pgoff, vma, to_kill);
> }
> }
> read_unlock(&tasklist_lock);
> @@ -550,7 +551,8 @@ static void collect_procs(struct page *page, struct list_head *tokill,
> if (PageAnon(page))
> collect_procs_anon(page, tokill, force_early);
> else
> - collect_procs_file(page, tokill, force_early);
> + collect_procs_file(page, page->mapping, page_to_pgoff(page),

Why not use page_mapping() helper here? It would be safer for THPs if they
ever get here...

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR