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Date: Tue, 29 Nov 2016 14:34:03 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org,
Ross Zwisler <ross.zwisler@...ux.intel.com>,
linux-ext4@...r.kernel.org, linux-mm@...ck.org,
linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 2/6] mm: Invalidate DAX radix tree entries only if
appropriate
Hi Jan,
On Thu, Nov 24, 2016 at 10:46:32AM +0100, Jan Kara wrote:
> @@ -452,16 +452,37 @@ void dax_wake_mapping_entry_waiter(struct address_space *mapping,
> __wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
> }
>
> +static int __dax_invalidate_mapping_entry(struct address_space *mapping,
> + pgoff_t index, bool trunc)
> +{
> + int ret = 0;
> + void *entry;
> + struct radix_tree_root *page_tree = &mapping->page_tree;
> +
> + spin_lock_irq(&mapping->tree_lock);
> + entry = get_unlocked_mapping_entry(mapping, index, NULL);
> + if (!entry || !radix_tree_exceptional_entry(entry))
> + goto out;
> + if (!trunc &&
> + (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) ||
> + radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)))
> + goto out;
> + radix_tree_delete(page_tree, index);
You could use the new __radix_tree_replace() here and save a second
tree lookup.
> +/*
> + * Invalidate exceptional DAX entry if easily possible. This handles DAX
> + * entries for invalidate_inode_pages() so we evict the entry only if we can
> + * do so without blocking.
> + */
> +int dax_invalidate_mapping_entry(struct address_space *mapping, pgoff_t index)
> +{
> + int ret = 0;
> + void *entry, **slot;
> + struct radix_tree_root *page_tree = &mapping->page_tree;
> +
> + spin_lock_irq(&mapping->tree_lock);
> + entry = __radix_tree_lookup(page_tree, index, NULL, &slot);
> + if (!entry || !radix_tree_exceptional_entry(entry) ||
> + slot_locked(mapping, slot))
> + goto out;
> + if (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) ||
> + radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> + goto out;
> + radix_tree_delete(page_tree, index);
Ditto for __radix_tree_replace().
> @@ -30,14 +30,6 @@ static void clear_exceptional_entry(struct address_space *mapping,
> struct radix_tree_node *node;
> void **slot;
>
> - /* Handled by shmem itself */
> - if (shmem_mapping(mapping))
> - return;
> -
> - if (dax_mapping(mapping)) {
> - dax_delete_mapping_entry(mapping, index);
> - return;
> - }
> spin_lock_irq(&mapping->tree_lock);
> /*
> * Regular page slots are stabilized by the page lock even
> @@ -70,6 +62,56 @@ static void clear_exceptional_entry(struct address_space *mapping,
> spin_unlock_irq(&mapping->tree_lock);
> }
>
> +/*
> + * Unconditionally remove exceptional entry. Usually called from truncate path.
> + */
> +static void truncate_exceptional_entry(struct address_space *mapping,
> + pgoff_t index, void *entry)
> +{
> + /* Handled by shmem itself */
> + if (shmem_mapping(mapping))
> + return;
> +
> + if (dax_mapping(mapping)) {
> + dax_delete_mapping_entry(mapping, index);
> + return;
> + }
> + clear_exceptional_entry(mapping, index, entry);
> +}
> +
> +/*
> + * Invalidate exceptional entry if easily possible. This handles exceptional
> + * entries for invalidate_inode_pages() so for DAX it evicts only unlocked and
> + * clean entries.
> + */
> +static int invalidate_exceptional_entry(struct address_space *mapping,
> + pgoff_t index, void *entry)
> +{
> + /* Handled by shmem itself */
> + if (shmem_mapping(mapping))
> + return 1;
> + if (dax_mapping(mapping))
> + return dax_invalidate_mapping_entry(mapping, index);
> + clear_exceptional_entry(mapping, index, entry);
> + return 1;
> +}
> +
> +/*
> + * Invalidate exceptional entry if clean. This handles exceptional entries for
> + * invalidate_inode_pages2() so for DAX it evicts only clean entries.
> + */
> +static int invalidate_exceptional_entry2(struct address_space *mapping,
> + pgoff_t index, void *entry)
> +{
> + /* Handled by shmem itself */
> + if (shmem_mapping(mapping))
> + return 1;
> + if (dax_mapping(mapping))
> + return dax_invalidate_clean_mapping_entry(mapping, index);
> + clear_exceptional_entry(mapping, index, entry);
> + return 1;
> +}
The way these functions are split out looks fine to me.
Now that clear_exceptional_entry() doesn't handle shmem and DAX
anymore, only shadows, could you rename it to clear_shadow_entry()?
The naming situation with truncate, invalidate, invalidate2 worries me
a bit. They aren't great names to begin with, but now DAX uses yet
another terminology for what state prevents a page from being dropped.
Can we switch to truncate, invalidate, and invalidate_sync throughout
truncate.c and then have DAX follow that naming too? Or maybe you can
think of better names. But neither invalidate2 and invalidate_clean
don't seem to capture it quite right ;)
Thanks
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