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Donenfeld" To: David Hildenbrand Cc: Linus Torvalds , linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de, linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , David Hildenbrand , linux-mm@kvack.org Subject: Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings Message-ID: References: <20240709130513.98102-2-Jason@zx2c4.com> <378f23cb-362e-413a-b221-09a5352e79f2@redhat.com> <9b400450-46bc-41c7-9e89-825993851101@redhat.com> <98798483-dfcd-451e-94bb-57d830bf68d8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <98798483-dfcd-451e-94bb-57d830bf68d8@redhat.com> X-Stat-Signature: e4eysw6hy4m5raytg1zr89upwzxx64qm X-Rspam-User: X-Rspamd-Queue-Id: D3D0E4001E X-Rspamd-Server: rspam02 X-HE-Tag: 1720720171-773985 X-HE-Meta: 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 +JozLoOH pzVl6L3f3sYtbFSe/CmBRpk8duTV0PFYdjZrR+UMZl0FNmClem2FTBdDrUwuoIHeSR73SWZ0uzr5RCHY0M9stoPEo0EIR4OZfYBpE9wqLFYhCxufa+Tnpht/UPAUPg4E2hgmAGBfg00GxSoTf9erNDxxmuVJL3+KTRw/KVHOFL4YvkZY7nscdFX6ZFQByw1saUKy1HxgBzt/nKdmaZSq+YubIAFZDQ7jCFkXzgAE9MW93VXBAffkG/88hTAbHRE2KXpYfxuPFWzMXLabnuhAHFn2TJbo37uV7hCntjQeot2WoTRXlx1h8NpvJxaXBn2tV9+Fix9fTh5tRWhARB3GZxEeIkqW7cXS62uoRFN2BYIpJFeIy29XdrwmGSQaf7Ap/CCKFP7uLNcEYGvseW7h1I0r+/EdyMy2zk0CDX3L7pzALB28HcaqmZfVGkvrIDWl2IXYecZlqIwpS79Q= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 11, 2024 at 07:24:33PM +0200, David Hildenbrand wrote: > On 11.07.24 19:17, Jason A. Donenfeld wrote: > > On Thu, Jul 11, 2024 at 07:09:36PM +0200, Jason A. Donenfeld wrote: > >> So, hmm... The swapbacked thing really seemed so simple... I wonder if > >> there's a way of recovering that. > > > > Not wanting to introduce a new bitflag, I went looking and noticed this: > > > > /* > > * Private page markings that may be used by the filesystem that owns the page > > * for its own purposes. > > * - PG_private and PG_private_2 cause release_folio() and co to be invoked > > */ > > PAGEFLAG(Private, private, PF_ANY) > > PAGEFLAG(Private2, private_2, PF_ANY) TESTSCFLAG(Private2, private_2, PF_ANY) > > PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY) > > TESTCLEARFLAG(OwnerPriv1, owner_priv_1, PF_ANY) > > > > The below +4/-1 diff is pretty hacky and might be illegal in the state > > of California, but I think it does work. The idea is that if that bit is > > normally only used for filesystems, then in the anonymous case, it's > > free to be used for this. > > > > Any opinions about this, or a suggestion on how to do that in a less > > ugly way? > > > > Jason > > > > > > diff --git a/mm/rmap.c b/mm/rmap.c > > index 1f9b5a9cb121..090554277e4a 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1403,6 +1403,8 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma, > > */ > > if (!(vma->vm_flags & VM_DROPPABLE)) > > __folio_set_swapbacked(folio); > > + else > > + folio_set_owner_priv_1(folio); > > > PG_owner_priv_1 maps to PG_swapcache? :) Oh, drat, it looks like this overloading is nothing new then.