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[209.85.220.65]) by mx.google.com with SMTPS id 8sor63086850qvi.5.2019.08.02.08.10.13 for (Google Transport Security); Fri, 02 Aug 2019 08:10:17 -0700 (PDT) Received-SPF: pass (google.com: domain of jwadams@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=TCfHoybp; spf=pass (google.com: domain of jwadams@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jwadams@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=sX2PNnPqRc1Vez9Gt0ymgNUdMb/B4mN+i8ZPfiL6UFc=; b=TCfHoybpUYB0q57sGjslZY0Qzg2W5zqXK9GXEpT81w3xFylA5VAxbe7I2hDdBlAkOw vZQBSCELRIJW8I77+ptRAHLm9EnjBBqrgcnn2911JFtYKIFpJMbyRxF4xP7jQfNzmuA4 Wl9Q2wfvPCIH2gL2kkaYx8aYF4kei6qLWvNFf0AJDgFtg5Utrhy7/oEPxz6cOpsjNb1G EPwdTu28JLG2EBx43Wln3+visWVuhE91Z/GQIQwQpHwKFxwy9BpHrECtjw+hKG/UNaiP FWMaVNBX9O2PAF7dPK4iEFIIilBFVP5mSpEwbINmhLQep6ln3P9Tn3TJjNohzzr7uDtB kN8w== X-Google-Smtp-Source: APXvYqzD/POmLm2vKfx6D1RC+luKxBQ/NjM0j2hWAxzv3R2JplpeeTrEROmYPNGnrMsBM/LkS1BimmH9BbnLMwr4jBw= X-Received: by 2002:a0c:b755:: with SMTP id q21mr95331996qve.92.1564758612071; Fri, 02 Aug 2019 08:10:12 -0700 (PDT) MIME-Version: 1.0 References: <20190802015332.229322-1-henryburns@google.com> In-Reply-To: <20190802015332.229322-1-henryburns@google.com> From: Jonathan Adams Date: Fri, 2 Aug 2019 08:09:35 -0700 Message-ID: Subject: Re: [PATCH 1/2] mm/zsmalloc.c: Migration can leave pages in ZS_EMPTY indefinitely To: Henry Burns Cc: Minchan Kim , Nitin Gupta , Sergey Senozhatsky , Shakeel Butt , Linux-MM , LKML Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000004, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Aug 1, 2019 at 6:53 PM Henry Burns wrote: > > In zs_page_migrate() we call putback_zspage() after we have finished > migrating all pages in this zspage. However, the return value is ignored. > If a zs_free() races in between zs_page_isolate() and zs_page_migrate(), > freeing the last object in the zspage, putback_zspage() will leave the page > in ZS_EMPTY for potentially an unbounded amount of time. > > To fix this, we need to do the same thing as zs_page_putback() does: > schedule free_work to occur. To avoid duplicated code, move the > sequence to a new putback_zspage_deferred() function which both > zs_page_migrate() and zs_page_putback() call. > > Signed-off-by: Henry Burns Reviewed-by: Jonathan Adams > > --- > mm/zsmalloc.c | 30 ++++++++++++++++++++---------- > 1 file changed, 20 insertions(+), 10 deletions(-) > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 1cda3fe0c2d9..efa660a87787 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1901,6 +1901,22 @@ static void dec_zspage_isolation(struct zspage *zspage) > zspage->isolated--; > } > > +static void putback_zspage_deferred(struct zs_pool *pool, > + struct size_class *class, > + struct zspage *zspage) > +{ > + enum fullness_group fg; > + > + fg = putback_zspage(class, zspage); > + /* > + * Due to page_lock, we cannot free zspage immediately > + * so let's defer. > + */ > + if (fg == ZS_EMPTY) > + schedule_work(&pool->free_work); > + > +} > + > static void replace_sub_page(struct size_class *class, struct zspage *zspage, > struct page *newpage, struct page *oldpage) > { > @@ -2070,7 +2086,7 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage, > * the list if @page is final isolated subpage in the zspage. > */ > if (!is_zspage_isolated(zspage)) > - putback_zspage(class, zspage); > + putback_zspage_deferred(pool, class, zspage); > > reset_page(page); > put_page(page); > @@ -2115,15 +2131,9 @@ static void zs_page_putback(struct page *page) > > spin_lock(&class->lock); > dec_zspage_isolation(zspage); > - if (!is_zspage_isolated(zspage)) { > - fg = putback_zspage(class, zspage); > - /* > - * Due to page_lock, we cannot free zspage immediately > - * so let's defer. > - */ > - if (fg == ZS_EMPTY) > - schedule_work(&pool->free_work); > - } > + if (!is_zspage_isolated(zspage)) > + putback_zspage_deferred(pool, class, zspage); > + > spin_unlock(&class->lock); > } > > -- > 2.22.0.770.g0f2c4a37fd-goog >