Page Cache Monitoring ( Hit/Miss )

Page Cache Monitoring ( Hit/Miss )

[Allan McAleavy]

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Hi Folks,

I am working on a rewrite of Brendan Greggs original cachestat (ftrace)
script into bcc. What I was looking for was a steer in the right direction
for what functions to trace. At present I trace the following.

add_to_page_cache_lru
account_page_dirtied
mark_page_accessed
mark_buffer_dirty

Where total = (mark_page_accessed - mark_buffer_dirty) & misses =
(add_to_page_cache_lru - account_page_dirtied), from this I then work out
the hit ratio etc. Is there any other key functions I should be tracing?

Thanks

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Re: Page Cache Monitoring ( Hit/Miss )

[Allan McAleavy]

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We add a page to the page cache using add_to_page_cache_lru based on the
following assumptions

READ MISS - So add an entry
no_cached_page - so we need to create one from
do_generic_file_read - during a file read operation
page_cache_read - calls add_to_page_cache_lru

CREATE A PAGE
struct page *__page_cache_alloc(gfp_t gfp)

page has flags which identify if dirty or free

Writes
add_to_page_cache
writepage / writepages
set_page_dirty_buffers
do_generic_mapping_read  - ASYNC read of pages in readahed?
__block_write_full_page

READ
find_get_pages


mark_page_accessed() for measuring cache accesses
mark_buffer_dirty() for measuring cache writes
add_to_page_cache_lru() for measuring page additions
account_page_dirtied() for measuring page dirties


 (mark_page_accessed - mark_buffer_dirty) & misses = (add_to_page_cache_lru
- account_page_dirtied),
 from this I then work out the hit ratio etc. Is there any other key
functions I should be tracing?

add_to_page_cache_lru
lru_cache_add
swap.c
filemap.c
vmscan.c

Functions used
lru_cache_add_active_or_unevictable
add_to_page_cache_lru
putback_lru_page

So best use lru_cache_add for additions.

account_page_dirtied() for measuring page dirties
set_page_dirty - calls above
__set_page_dirty_nobuffers - calls above also

mark_buffer_dirty() for measuring cache writes - this calls
__set_page_dirty ( are we getting twice the calls here? )
mark_page_accessed - calls SetPageActive

On Thu, Dec 10, 2015 at 9:42 AM, Allan McAleavy <allan.mcaleavy@gmail.com>
wrote:

> Hi Folks,
>
> I am working on a rewrite of Brendan Greggs original cachestat (ftrace)
> script into bcc. What I was looking for was a steer in the right direction
> for what functions to trace. At present I trace the following.
>
> add_to_page_cache_lru
> account_page_dirtied
> mark_page_accessed
> mark_buffer_dirty
>
> Where total = (mark_page_accessed - mark_buffer_dirty) & misses =
> (add_to_page_cache_lru - account_page_dirtied), from this I then work out
> the hit ratio etc. Is there any other key functions I should be tracing?
>
> Thanks
>

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