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Move readahead and dropbehind fault functionality into a helper routine for

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clarity.

Reviewed by:	dougm, kib, markj
Differential Revision:	https://reviews.freebsd.org/D23282
This commit is contained in:
Jeff Roberson 2020-01-21 00:12:57 +00:00
parent 825a73c36f
commit 5949b1ca8c
1 changed files with 58 additions and 40 deletions
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98
sys/vm/vm_fault.c
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@ -120,6 +120,7 @@ __FBSDID("$FreeBSD$");
#define VM_FAULT_DONTNEED_MIN 1048576
struct faultstate {
vm_offset_t vaddr;
vm_page_t m;
vm_page_t m_cow;
vm_object_t object;
@ -679,6 +680,59 @@ vm_fault_lock_vnode(struct faultstate *fs, bool objlocked)
return (KERN_RESOURCE_SHORTAGE);
}
/*
* Calculate the desired readahead. Handle drop-behind.
*
* Returns the number of readahead blocks to pass to the pager.
*/
static int
vm_fault_readahead(struct faultstate *fs)
{
int era, nera;
u_char behavior;
KASSERT(fs->lookup_still_valid, ("map unlocked"));
era = fs->entry->read_ahead;
behavior = vm_map_entry_behavior(fs->entry);
if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
nera = 0;
} else if (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL) {
nera = VM_FAULT_READ_AHEAD_MAX;
if (fs->vaddr == fs->entry->next_read)
vm_fault_dontneed(fs, fs->vaddr, nera);
} else if (fs->vaddr == fs->entry->next_read) {
/*
* This is a sequential fault. Arithmetically
* increase the requested number of pages in
* the read-ahead window. The requested
* number of pages is "# of sequential faults
* x (read ahead min + 1) + read ahead min"
*/
nera = VM_FAULT_READ_AHEAD_MIN;
if (era > 0) {
nera += era + 1;
if (nera > VM_FAULT_READ_AHEAD_MAX)
nera = VM_FAULT_READ_AHEAD_MAX;
}
if (era == VM_FAULT_READ_AHEAD_MAX)
vm_fault_dontneed(fs, fs->vaddr, nera);
} else {
/*
* This is a non-sequential fault.
*/
nera = 0;
}
if (era != nera) {
/*
* A read lock on the map suffices to update
* the read ahead count safely.
*/
fs->entry->read_ahead = nera;
}
return (nera);
}
/*
* Wait/Retry if the page is busy. We have to do this if the page is
* either exclusive or shared busy because the vm_pager may be using
@ -725,7 +779,7 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
vm_offset_t e_end, e_start;
vm_pindex_t retry_pindex;
vm_prot_t prot, retry_prot;
int ahead, alloc_req, behind, cluster_offset, era, faultcount;
int ahead, alloc_req, behind, cluster_offset, faultcount;
int nera, oom, result, rv;
u_char behavior;
boolean_t wired; /* Passed by reference. */
@ -737,6 +791,7 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
return (KERN_PROTECTION_FAILURE);
fs.vp = NULL;
fs.vaddr = vaddr;
faultcount = 0;
nera = -1;
hardfault = false;
@ -989,45 +1044,7 @@ readrest:
* apply to subsequent objects in the shadow chain.
*/
if (nera == -1 && !P_KILLED(curproc)) {
KASSERT(fs.lookup_still_valid, ("map unlocked"));
era = fs.entry->read_ahead;
behavior = vm_map_entry_behavior(fs.entry);
if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
nera = 0;
} else if (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL) {
nera = VM_FAULT_READ_AHEAD_MAX;
if (vaddr == fs.entry->next_read)
vm_fault_dontneed(&fs, vaddr, nera);
} else if (vaddr == fs.entry->next_read) {
/*
* This is a sequential fault. Arithmetically
* increase the requested number of pages in
* the read-ahead window. The requested
* number of pages is "# of sequential faults
* x (read ahead min + 1) + read ahead min"
*/
nera = VM_FAULT_READ_AHEAD_MIN;
if (era > 0) {
nera += era + 1;
if (nera > VM_FAULT_READ_AHEAD_MAX)
nera = VM_FAULT_READ_AHEAD_MAX;
}
if (era == VM_FAULT_READ_AHEAD_MAX)
vm_fault_dontneed(&fs, vaddr, nera);
} else {
/*
* This is a non-sequential fault.
*/
nera = 0;
}
if (era != nera) {
/*
* A read lock on the map suffices to update
* the read ahead count safely.
*/
fs.entry->read_ahead = nera;
}
nera = vm_fault_readahead(&fs);
/*
* Prepare for unlocking the map. Save the map
* entry's start and end addresses, which are used to
@ -1038,6 +1055,7 @@ readrest:
*/
e_start = fs.entry->start;
e_end = fs.entry->end;
behavior = vm_map_entry_behavior(fs.entry);
}
/*