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GAmWN/28Tix3V6ACcEFQNDT2YdECzoWYa/Dcf75+TQcSVWiMgfoj4L0z6hoLPL1iI+B8vmvsyIV4Y+M7ue/o+//OTkOEsvLHWbukcTrAT9jHWwCaQs4BhJofLQcUy0T5X7DooKffCpo8FNEVQOqk5VPJ6ghN5jE/JQyO/bNj2bgoZZwxSc8rcNAKqBdcTFcuCb2Bb9uieuYzviNFGESs31yMPFBaSypQG5nTUMlo1p0H7GNsATMVx5TR4DboV1nOJ1nVhYUdrk2kdgkg= 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: John Hubbard writes: > On 10/18/24 12:47 AM, David Hildenbrand wrote: >> On 18.10.24 03:17, John Hubbard wrote: [...] > And actually this whole thing of "pin the pages, just for a short time, e= ven > though you're not allowed to" is partly why this area is so entertaining. I'm looking at your v3 but as an aside I disagree with this statement. AFAIK you're always allowed to pin the pages for a short time (ie. !FOLL_LONGTERM), or did I misunderstand your comment? >> diff --git a/mm/gup.c b/mm/gup.c >> index a82890b46a36..81fc8314e687 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -2403,8 +2403,9 @@ static int migrate_longterm_unpinnable_folios( >> =C2=A0 * -EAGAIN. The caller should re-pin the entire range with >> FOLL_PIN and then >> =C2=A0 * call this routine again. >> =C2=A0 * >> - * If an error other than -EAGAIN occurs, this indicates a >> migration failure. >> - * The caller should give up, and propagate the error back up the >> call stack. >> + * If an error occurs, all folios are unpinned. If an error other than >> + * -EAGAIN occurs, this indicates a migration failure. The caller >> should give >> + * up, and propagate the error back up the call stack. >> =C2=A0 * >> =C2=A0 * If everything is OK and all folios in the range are allowed to >> be pinned, >> =C2=A0 * then this routine leaves all folios pinned and returns zero fo= r >> success. >> @@ -2437,8 +2438,10 @@ static long >> check_and_migrate_movable_pages(unsigned long nr_pages, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 long i, ret; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 folios =3D kmalloc_array(nr_= pages, sizeof(*folios), >> GFP_KERNEL); >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!folios) >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!folios) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 unpin_user_pages(pages, nr_pages); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 return -ENOMEM; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 for (i =3D 0; i < nr_pages; = i++) >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 folios[i] =3D page_folio(pages[i]); >> Then, check_and_migrate_movable_pages() will never return with an >> error and >> having folios pinned. >> If check_and_migrate_movable_pages() -> >> check_and_migrate_movable_folios() >> returns "0", all folios remain pinned an no harm is done. >> Consequently, I think patch #2 is not really required, because it >> doesn't >> perform the temporary allocation that could fail with -ENOMEM. >>=20 > > Yes! > >> Sorry for taking a closer look only now ... >>=20 > > It's all still in review, so the timing is perfectly fine. I really > appreciate the closer look, it's definitely making things better. > > > thanks,