Re: [PATCH] improve read ahead in kernel

[Randy Dunlap]

On 12/09/12 07:57, xtu4 wrote:
> 
> Subject: [PATCH] when system in low memory scenario, imaging there is a mp3
>  play, or video play, we need to read mp3 or video file
>  from memory to page cache,but when system lack of memory,
>  page cache of mp3 or video file will be reclaimed.once read
>  in memory, then reclaimed, it will cause audio or video
>  glitch,and it will increase the io operation at the same
>  time.
> 
> Signed-off-by: xiaobing tu <xiaobing.tu@xxxxxxxxx>

What tree does this patch apply to?

It looks like most (or all) of the tabs in the source files have
been changed to spaces, which is Not Good.
Maybe some info in Documentation/email-clients.txt could help you.

> ---
>  include/linux/mm_types.h |    4 ++++
>  mm/Kconfig               |    6 ++++++
>  mm/filemap.c             |    4 ++++
>  mm/readahead.c           |   20 +++++++++++++++++---
>  mm/vmscan.c              |   10 ++++++++--
>  5 files changed, 39 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5b42f1b..541864d 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -149,6 +149,10 @@ struct page {
>       */
>      void *shadow;
>  #endif
> +#ifdef CONFIG_LOWMEMORY_READAHEAD
> +    unsigned int ioprio;
> +#endif
> +
>  }
>  /*
>   * If another subsystem starts using the double word pairing for atomic
> diff --git a/mm/Kconfig b/mm/Kconfig
> index e338407..dade8d3 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -140,6 +140,12 @@ config ARCH_DISCARD_MEMBLOCK
>  config NO_BOOTMEM
>      boolean
> 
> +# improve readahead in low memory scenario
> +config LOWMEMORY_READAHEAD
> +    bool "improve readahead in low memory scenario"
> +    depends on (IA64 || X86)

Why this depends on?
I don't see anything that is arch-specific in the patch.


> +
> +
>  # eventually, we can have this option just 'select SPARSEMEM'
>  config MEMORY_HOTPLUG
>      bool "Allow for memory hot-add"
> diff --git a/mm/filemap.c b/mm/filemap.c
> index a0701e6..e32efed8 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -129,6 +129,10 @@ void __delete_from_page_cache(struct page *page)
>      page->mapping = NULL;
>      /* Leave page->index set: truncation lookup relies upon it */
>      mapping->nrpages--;
> +    #ifdef CONFIG_LOWMEMORY_READAHEAD
> +    page->ioprio = 0;
> +    #endif
> +
>      __dec_zone_page_state(page, NR_FILE_PAGES);
>      if (PageSwapBacked(page))
>          __dec_zone_page_state(page, NR_SHMEM);
> diff --git a/mm/readahead.c b/mm/readahead.c
> index cbcbb02..dd07cfe 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -159,6 +159,11 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
>      int page_idx;
>      int ret = 0;
>      loff_t isize = i_size_read(inode);
> +#ifdef CONFIG_LOWMEMORY_READAHEAD
> +    int class = 0;
> +    if (p->io_context)
> +    class = IOPRIO_PRIO_CLASS(p->io_context->ioprio);
> +#endif
> 
>      if (isize == 0)
>          goto out;
> @@ -177,12 +182,21 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
>          rcu_read_lock();
>          page = radix_tree_lookup(&mapping->page_tree, page_offset);
>          rcu_read_unlock();
> -        if (page)
> -            continue;
> -
> +        if (page){
> +#ifdef CONFIG_LOWMEMORY_READAHEAD
> +            if (class == IOPRIO_CLASS_RT) {
> +                page->ioprio = 1;
> +#endif
> +                continue;
> +            }
>          page = page_cache_alloc_readahead(mapping);
>          if (!page)
>              break;
> +#ifdef CONFIG_LOWMEMORY_READAHEAD
> +        if (class == IOPRIO_CLASS_RT) {
> +            page->ioprio = 1;
> +#endif
> +
>          page->index = page_offset;
>          list_add(&page->lru, &page_pool);
>          if (page_idx == nr_to_read - lookahead_size)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 753a2dc..86e03aa 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -728,8 +728,14 @@ static enum page_references page_check_references(struct page *page,
>      }
> 
>      /* Reclaim if clean, defer dirty pages to writeback */
> -    if (referenced_page && !PageSwapBacked(page))
> -        return PAGEREF_RECLAIM_CLEAN;
> +    if (referenced_page && !PageSwapBacked(page)) {
> +#ifdef CONFIG_LOWMEMORY_READAHEAD
> +        if (page->ioprio == 1) {
> +            return PAGEREF_ACTIVATE;
> +        } else
> +#endif
> +            return PAGEREF_RECLAIM_CLEAN;
> +    }
> 
>      return PAGEREF_RECLAIM;
>  }


-- 
~Randy
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