Author: will
Date: Sat Apr 11 18:51:41 2015
New Revision: 281442
URL: https://svnweb.freebsd.org/changeset/base/281442
Log:
uiomove_object_page(): Avoid instantiating pages in sparse regions on reads.
Check whether the page being requested is either resident or on swap. If
not, read from the zero_region instead of instantiating an unnecessary page.
This avoids consuming memory for sparse files on tmpfs, when they are read
by applications that do not use SEEK_HOLE/SEEK_DATA (which is most of them).
Reviewed by: kib
MFC after: 1 week
Sponsored by: Spectra Logic
Modified:
head/sys/kern/uipc_shm.c
Modified: head/sys/kern/uipc_shm.c
==============================================================================
--- head/sys/kern/uipc_shm.c Sat Apr 11 18:45:22 2015 (r281441)
+++ head/sys/kern/uipc_shm.c Sat Apr 11 18:51:41 2015 (r281442)
@@ -163,6 +163,17 @@ uiomove_object_page(vm_object_t obj, siz
VM_OBJECT_WLOCK(obj);
/*
+ * Read I/O without either a corresponding resident page or swap
+ * page: use zero_region. This is intended to avoid instantiating
+ * pages on read from a sparse region.
+ */
+ if (uio->uio_rw == UIO_READ && vm_page_lookup(obj, idx) == NULL &&
+ !vm_pager_has_page(obj, idx, NULL, NULL)) {
+ VM_OBJECT_WUNLOCK(obj);
+ return (uiomove(__DECONST(void *, zero_region), len, uio));
+ }
+
+ /*
* Parallel reads of the page content from disk are prevented
* by exclusive busy.
*
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