Re: mm: swapin read-ahead and zram

[Sergey Senozhatsky]

On (25/08/15 14:51), Sergey Senozhatsky wrote:
[..]
> For instance, notice how entry 1615265 is read, decompressed, then
> presumably evicted from the memory, and read/decompressed again
> soon after, almost immediately.  Also notice how that entry 1615265
> has already went through this cycle 189 times.  It's not entirely
> clear why this happens.
> 
> As far as I can tell, it seems that these extra zram reads are coming from
> the swapin read-ahead:
>  handle_mm_fault
>   do_swap_page
>    swapin_readahead
>     swap_read_folio
>      submit_bio_wait
>       submit_bio_noacct_nocheck
>        __submit_bio
>         zram_submit_bio
>          zram_read_page
>           zram_read_from_zspool

Sorry, I need to correct myself here, it seems that read-ahead win is 1
pretty much all the time in swap_vma_readahead(), so that's probably not
read-ahead after all.