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Re: [PATCH V4 4/6] mm: reclaim MADV_FREE pages

From Johannes Weiner <hannes@cmpxchg.org>
Newsgroups linux.kernel
Subject Re: [PATCH V4 4/6] mm: reclaim MADV_FREE pages
Date 2017-02-24 16:50 +0100
Message-ID <teqi6-2bp-25@gated-at.bofh.it> (permalink)
References <tdKiR-62X-7@gated-at.bofh.it> <tdKiT-62X-49@gated-at.bofh.it> <tedEd-1M7-5@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Fri, Feb 24, 2017 at 11:12:18AM +0900, Minchan Kim wrote:
> > @@ -1525,8 +1531,8 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
> >  
> >  	if (ret != SWAP_MLOCK && !page_mapcount(page)) {
> >  		ret = SWAP_SUCCESS;
> > -		if (rp.lazyfreed && !PageDirty(page))
> > -			ret = SWAP_LZFREE;
> > +		if (rp.lazyfreed && PageDirty(page))
> > +			ret = SWAP_DIRTY;
> 
> Hmm, I don't understand why we need to introduce new return value.
> Can't we set SetPageSwapBacked and return SWAP_FAIL in try_to_unmap_one?

I think that's a bad idea. A function called "try_to_unmap" shouldn't
have as a side effect that it changes the page's LRU type in an error
case. Let try_to_unmap be about unmapping the page. If it fails, make
it report why and let the caller deal with the fallout. Any LRU fixups
are much better placed in vmscan.c.

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Thread

[PATCH V4 0/6] mm: fix some MADV_FREE issues Shaohua Li <shli@fb.com> - 2017-02-22 20:00 +0100
  [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE list Shaohua Li <shli@fb.com> - 2017-02-22 20:00 +0100
    Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE  list Johannes Weiner <hannes@cmpxchg.org> - 2017-02-23 17:10 +0100
      Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE  list Johannes Weiner <hannes@cmpxchg.org> - 2017-02-23 20:00 +0100
    Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE  list Minchan Kim <minchan@kernel.org> - 2017-02-24 03:00 +0100
      Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE  list Minchan Kim <minchan@kernel.org> - 2017-02-25 00:40 +0100
  [PATCH V4 5/6] mm: enable MADV_FREE for swapless system Shaohua Li <shli@fb.com> - 2017-02-22 20:00 +0100
  [PATCH V4 2/6] mm: don't assume anonymous pages have SwapBacked flag Shaohua Li <shli@fb.com> - 2017-02-22 20:00 +0100
  [PATCH V4 4/6] mm: reclaim MADV_FREE pages Shaohua Li <shli@fb.com> - 2017-02-22 20:00 +0100
    Re: [PATCH V4 4/6] mm: reclaim MADV_FREE pages Johannes Weiner <hannes@cmpxchg.org> - 2017-02-23 17:20 +0100
    Re: [PATCH V4 4/6] mm: reclaim MADV_FREE pages Minchan Kim <minchan@kernel.org> - 2017-02-24 03:20 +0100
      Re: [PATCH V4 4/6] mm: reclaim MADV_FREE pages Johannes Weiner <hannes@cmpxchg.org> - 2017-02-24 16:50 +0100
        Re: [PATCH V4 4/6] mm: reclaim MADV_FREE pages Minchan Kim <minchan@kernel.org> - 2017-02-25 00:30 +0100

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