linux-kernel - Re: [PATCH 1/2] zram: introduce compressed data writeback

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Message-ID: <dt632m4jh2jt5fhnddcbgtdndxh6552hcbwpqeklfx6z7oaihz@lnhskip6whc6>
Date: Mon, 1 Dec 2025 18:09:37 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Barry Song <21cnbao@...il.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Richard Chang <richardycc@...gle.com>, 
	Brian Geffon <bgeffon@...gle.com>, Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, linux-block@...r.kernel.org, Minchan Kim <minchan@...gle.com>
Subject: Re: [PATCH 1/2] zram: introduce compressed data writeback

On (25/12/01 16:59), Barry Song wrote:
> On Mon, Dec 1, 2025 at 11:56 AM Sergey Senozhatsky
> <senozhatsky@...omium.org> wrote:
> [...]
> > > > zram stores all written back slots raw, which implies that
> > > > during writeback zram first has to decompress slots (except
> > > > for ZRAM_HUGE slots, which are raw already).  The problem
> > > > with this approach is that not every written back page gets
> > > > read back (either via read() or via page-fault), which means
> > > > that zram basically wastes CPU cycles and battery decompressing
> > > > such slots.  This changes with introduction of decompression
> > >
> > > If a page is swapped out and never read again, does that actually indicate
> > > a memory leak in userspace?
> >
> > No, it just means that there is no page-fault on that page.  E.g. we
> > swapped out an unused browser tab and never come back to it within the
> > session: e.g. user closed the tab/app, or logged out of session, or
> > rebooted the device, or simply powered off (desktop/laptop).
> 
> Thanks, Sergey. That makes sense to me. On Android, users don’t have a
> close button, yet apps can still be OOM-killed; those pages are never
> swapped in.

I see.  I suppose on android you still can swipe up and terminate
un-needed apps, wouldn't this be the same?  Well, apart from that,
zram is not android-specific, some distros use it on desktops/laptops
as well.