Messages in this thread | | | Date | Sun, 4 Mar 2012 09:51:01 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH] mm: shmem: unlock valid page |
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On Sun, 4 Mar 2012, Hillf Danton wrote: > In shmem_read_mapping_page_gfp() page is unlocked if no error returned, > so the unlocked page has to valid. > > To guarantee that validity, when getting page, success result is feed > back to caller only when page is valid. > > Signed-off-by: Hillf Danton <dhillf@gmail.com>
I don't understand your description, nor its relation to the patch.
NAK to the patch: when no page has previously been allocated, the SGP_READ case avoids allocation and returns NULL - do_shmem_file_read then copies the ZERO_PAGE instead, avoiding lots of unnecessary memory allocation when reading a large sparse file.
Hugh
> --- > > --- a/mm/shmem.c Sun Mar 4 12:17:42 2012 > +++ b/mm/shmem.c Sun Mar 4 12:26:56 2012 > @@ -889,13 +889,13 @@ repeat: > goto failed; > } > > - if (page || (sgp == SGP_READ && !swap.val)) { > + if (page) { > /* > * Once we can get the page lock, it must be uptodate: > * if there were an error in reading back from swap, > * the page would not be inserted into the filecache. > */ > - BUG_ON(page && !PageUptodate(page)); > + BUG_ON(!PageUptodate(page)); > *pagep = page; > return 0; > } > -- >
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